diff --git a/apm/package.json b/apm/package.json
index 84f73451d..e7a0c8fdc 100644
--- a/apm/package.json
+++ b/apm/package.json
@@ -6,6 +6,6 @@
     "url": "https://github.com/atom/atom.git"
   },
   "dependencies": {
-    "atom-package-manager": "0.157.0"
+    "atom-package-manager": "0.158.0"
   }
 }
diff --git a/build/Gruntfile.coffee b/build/Gruntfile.coffee
index 071dd1295..7c687ac92 100644
--- a/build/Gruntfile.coffee
+++ b/build/Gruntfile.coffee
@@ -223,7 +223,7 @@ module.exports = (grunt) ->
 
   ciTasks = ['output-disk-space', 'download-atom-shell', 'download-atom-shell-chromedriver', 'build']
   ciTasks.push('dump-symbols') if process.platform isnt 'win32'
-  ciTasks.push('set-version', 'check-licenses', 'lint')
+  ciTasks.push('set-version', 'check-licenses', 'lint', 'generate-asar')
   ciTasks.push('mkdeb') if process.platform is 'linux'
   ciTasks.push('create-windows-installer') if process.platform is 'win32'
   ciTasks.push('test') if process.platform is 'darwin'
@@ -231,6 +231,6 @@ module.exports = (grunt) ->
   ciTasks.push('publish-build') unless process.env.TRAVIS
   grunt.registerTask('ci', ciTasks)
 
-  defaultTasks = ['download-atom-shell', 'download-atom-shell-chromedriver', 'build', 'set-version']
+  defaultTasks = ['download-atom-shell', 'download-atom-shell-chromedriver', 'build', 'set-version', 'generate-asar']
   defaultTasks.push 'install' unless process.platform is 'linux'
   grunt.registerTask('default', defaultTasks)
diff --git a/build/package.json b/build/package.json
index 212f9c3ed..3f0a3caef 100644
--- a/build/package.json
+++ b/build/package.json
@@ -6,13 +6,14 @@
     "url": "https://github.com/atom/atom.git"
   },
   "dependencies": {
+    "asar": "^0.4.4",
     "async": "~0.2.9",
     "donna": "1.0.10",
     "formidable": "~1.0.14",
     "fs-plus": "2.x",
     "github-releases": "~0.2.0",
     "grunt": "~0.4.1",
-    "grunt-atom-shell-installer": "^0.28.0",
+    "grunt-atom-shell-installer": "^0.29.0",
     "grunt-cli": "~0.1.9",
     "grunt-coffeelint": "git+https://github.com/atom/grunt-coffeelint.git#cfb99aa99811d52687969532bd5a98011ed95bfe",
     "grunt-contrib-coffee": "~0.12.0",
@@ -31,7 +32,7 @@
     "request": "~2.27.0",
     "rimraf": "~2.2.2",
     "runas": "^2",
-    "tello": "1.0.4",
+    "tello": "1.0.5",
     "temp": "~0.8.1",
     "underscore-plus": "1.x",
     "unzip": "~0.1.9",
diff --git a/build/tasks/build-task.coffee b/build/tasks/build-task.coffee
index a94b38f75..3411f4dae 100644
--- a/build/tasks/build-task.coffee
+++ b/build/tasks/build-task.coffee
@@ -22,7 +22,7 @@ module.exports = (grunt) ->
     mkdir appDir
 
     if process.platform isnt 'win32'
-      cp 'atom.sh', path.join(appDir, 'atom.sh')
+      cp 'atom.sh', path.resolve(appDir, '..', 'new-app', 'atom.sh')
 
     cp 'package.json', path.join(appDir, 'package.json')
 
@@ -65,6 +65,7 @@ module.exports = (grunt) ->
       path.join('jasmine-node', 'node_modules', 'gaze')
       path.join('jasmine-node', 'spec')
       path.join('node_modules', 'nan')
+      path.join('node_modules', 'native-mate')
       path.join('build', 'binding.Makefile')
       path.join('build', 'config.gypi')
       path.join('build', 'gyp-mac-tool')
@@ -143,13 +144,13 @@ module.exports = (grunt) ->
     for directory in packageDirectories
       cp directory, path.join(appDir, directory), filter: filterPackage
 
-    cp 'spec', path.join(appDir, 'spec')
+    cp 'spec', path.join(appDir, 'spec'), filter: /fixtures|integration|.+-spec\.coffee/
     cp 'src', path.join(appDir, 'src'), filter: /.+\.(cson|coffee)$/
     cp 'static', path.join(appDir, 'static')
 
-    cp path.join('apm', 'node_modules', 'atom-package-manager'), path.join(appDir, 'apm'), filter: filterNodeModule
+    cp path.join('apm', 'node_modules', 'atom-package-manager'), path.resolve(appDir, '..', 'new-app', 'apm'), filter: filterNodeModule
     if process.platform isnt 'win32'
-      fs.symlinkSync(path.join('..', '..', 'bin', 'apm'), path.join(appDir, 'apm', 'node_modules', '.bin', 'apm'))
+      fs.symlinkSync(path.join('..', '..', 'bin', 'apm'), path.resolve(appDir, '..', 'new-app', 'apm', 'node_modules', '.bin', 'apm'))
 
     if process.platform is 'darwin'
       grunt.file.recurse path.join('resources', 'mac'), (sourcePath, rootDirectory, subDirectory='', filename) ->
diff --git a/build/tasks/generate-asar-task.coffee b/build/tasks/generate-asar-task.coffee
new file mode 100644
index 000000000..a71d88dfe
--- /dev/null
+++ b/build/tasks/generate-asar-task.coffee
@@ -0,0 +1,35 @@
+asar = require 'asar'
+fs = require 'fs'
+path = require 'path'
+
+module.exports = (grunt) ->
+  {cp, rm} = require('./task-helpers')(grunt)
+
+  grunt.registerTask 'generate-asar', 'Generate asar archive for the app', ->
+    done = @async()
+
+    unpack = [
+      '*.node'
+      '.ctags'
+      'ctags-darwin'
+      'ctags-linux'
+      'ctags-win32.exe'
+    ]
+    unpack = "{#{unpack.join(',')}}"
+
+    appDir = grunt.config.get('atom.appDir')
+    unless fs.existsSync(appDir)
+      grunt.log.error 'The app has to be built before generating asar archive.'
+      return done(false)
+
+    asar.createPackageWithOptions appDir, path.resolve(appDir, '..', 'app.asar'), {unpack}, (err) ->
+      return done(err) if err?
+
+      rm appDir
+      fs.renameSync path.resolve(appDir, '..', 'new-app'), appDir
+
+      ctagsFolder = path.join("#{appDir}.asar.unpacked", 'node_modules', 'symbols-view', 'vendor')
+      for ctagsFile in fs.readdirSync(ctagsFolder)
+        fs.chmodSync(path.join(ctagsFolder, ctagsFile), "755")
+
+      done()
diff --git a/build/tasks/generate-license-task.coffee b/build/tasks/generate-license-task.coffee
index 6b616f5cb..eaf1a9a66 100644
--- a/build/tasks/generate-license-task.coffee
+++ b/build/tasks/generate-license-task.coffee
@@ -17,7 +17,7 @@ module.exports = (grunt) ->
 
       licenseText = getLicenseText(dependencyLicenses)
       if mode is 'save'
-        targetPath = path.join(grunt.config.get('atom.appDir'), 'LICENSE.md')
+        targetPath = path.resolve(grunt.config.get('atom.appDir'), '..', 'LICENSE.md')
         fs.writeFileSync(targetPath, licenseText)
       else
         console.log licenseText
diff --git a/package.json b/package.json
index 8fd36d5bd..744994a8f 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "atom",
   "productName": "Atom",
-  "version": "0.192.0",
+  "version": "0.193.0",
   "description": "A hackable text editor for the 21st Century.",
   "main": "./src/browser/main.js",
   "repository": {
@@ -113,7 +113,7 @@
     "settings-view": "0.192.0",
     "snippets": "0.88.0",
     "spell-check": "0.55.0",
-    "status-bar": "0.68.0",
+    "status-bar": "0.69.0",
     "styleguide": "0.44.0",
     "symbols-view": "0.94.0",
     "tabs": "0.67.0",
@@ -128,9 +128,9 @@
     "language-coffee-script": "0.39.0",
     "language-csharp": "0.5.0",
     "language-css": "0.28.0",
-    "language-gfm": "0.68.0",
+    "language-gfm": "0.69.0",
     "language-git": "0.10.0",
-    "language-go": "0.23.0",
+    "language-go": "0.25.0",
     "language-html": "0.32.0",
     "language-hyperlink": "0.12.2",
     "language-java": "0.14.0",
diff --git a/script/mkdeb b/script/mkdeb
index 272fe23f3..c39b6d649 100755
--- a/script/mkdeb
+++ b/script/mkdeb
@@ -33,7 +33,7 @@ cp "$ICON_FILE" "$TARGET/usr/share/pixmaps"
 
 # Copy generated LICENSE.md to /usr/share/doc/atom/copyright
 mkdir -m $FILE_MODE -p "$TARGET/usr/share/doc/atom"
-cp "$TARGET/usr/share/atom/resources/app/LICENSE.md" "$TARGET/usr/share/doc/atom/copyright"
+cp "$TARGET/usr/share/atom/resources/LICENSE.md" "$TARGET/usr/share/doc/atom/copyright"
 
 # Add lintian overrides
 mkdir -m $FILE_MODE -p "$TARGET/usr/share/lintian/overrides"
diff --git a/spec/atom-spec.coffee b/spec/atom-spec.coffee
index a293edccd..99a7f432e 100644
--- a/spec/atom-spec.coffee
+++ b/spec/atom-spec.coffee
@@ -139,7 +139,7 @@ describe "the `atom` global", ->
         windowState: null
 
       spyOn(Atom, 'getLoadSettings').andCallFake -> loadSettings
-      spyOn(Atom, 'getStorageDirPath').andReturn(temp.mkdirSync("storage-dir-"))
+      spyOn(Atom.getStorageFolder(), 'getPath').andReturn(temp.mkdirSync("storage-dir-"))
 
       atom.mode = "editor"
       atom.state.stuff = "cool"
diff --git a/spec/fixtures/packages/theme-with-invalid-styles/index.less b/spec/fixtures/packages/theme-with-invalid-styles/index.less
new file mode 100644
index 000000000..b554d9e46
--- /dev/null
+++ b/spec/fixtures/packages/theme-with-invalid-styles/index.less
@@ -0,0 +1 @@
+<>
diff --git a/spec/fixtures/packages/theme-with-invalid-styles/package.json b/spec/fixtures/packages/theme-with-invalid-styles/package.json
new file mode 100644
index 000000000..1dd1ee48b
--- /dev/null
+++ b/spec/fixtures/packages/theme-with-invalid-styles/package.json
@@ -0,0 +1,4 @@
+{
+  "name": "theme-with-invalid-styles",
+  "theme": "ui"
+}
diff --git a/spec/integration/helpers/start-atom.coffee b/spec/integration/helpers/start-atom.coffee
index 08d3659c3..0de6644b3 100644
--- a/spec/integration/helpers/start-atom.coffee
+++ b/spec/integration/helpers/start-atom.coffee
@@ -108,6 +108,15 @@ buildAtomClient = (args, env) ->
           ]), env: extend({}, process.env, env))
         done()
 
+    .addCommand "dispatchCommand", (command, done) ->
+      @execute "atom.commands.dispatch(document.activeElement, '#{command}')"
+      .call(done)
+
+    .addCommand "simulateQuit", (done) ->
+      @execute -> atom.unloadEditorWindow()
+      .execute -> require("remote").require("app").emit("before-quit")
+      .call(done)
+
 module.exports = (args, env, fn) ->
   [chromedriver, chromedriverLogs, chromedriverExit] = []
 
@@ -133,6 +142,7 @@ module.exports = (args, env, fn) ->
   waitsFor("webdriver to finish", (done) ->
     finish = once ->
       client
+        .simulateQuit()
         .end()
         .then(-> chromedriver.kill())
         .then(chromedriverExit.then(
@@ -147,7 +157,7 @@ module.exports = (args, env, fn) ->
     client = buildAtomClient(args, env)
 
     client.on "error", (err) ->
-      jasmine.getEnv().currentSpec.fail(JSON.stringify(err))
+      jasmine.getEnv().currentSpec.fail(new Error(err.response?.body?.value?.message))
       finish()
 
     fn(client.init()).then(finish)
diff --git a/spec/integration/startup-spec.coffee b/spec/integration/startup-spec.coffee
index e0df3ad9b..2dcf6ba38 100644
--- a/spec/integration/startup-spec.coffee
+++ b/spec/integration/startup-spec.coffee
@@ -6,22 +6,22 @@ return unless process.env.ATOM_INTEGRATION_TESTS_ENABLED
 fs = require "fs"
 path = require "path"
 temp = require("temp").track()
-AtomHome = temp.mkdirSync('atom-home')
-fs.writeFileSync(path.join(AtomHome, 'config.cson'), fs.readFileSync(path.join(__dirname, 'fixtures', 'atom-home', 'config.cson')))
 runAtom = require("./helpers/start-atom")
 
 describe "Starting Atom", ->
-  [tempDirPath, otherTempDirPath] = []
+  [tempDirPath, otherTempDirPath, atomHome] = []
 
   beforeEach ->
     jasmine.useRealClock()
 
+    atomHome = temp.mkdirSync('atom-home')
+    fs.writeFileSync(path.join(atomHome, 'config.cson'), fs.readFileSync(path.join(__dirname, 'fixtures', 'atom-home', 'config.cson')))
     tempDirPath = temp.mkdirSync("empty-dir")
     otherTempDirPath = temp.mkdirSync("another-temp-dir")
 
   describe "opening a new file", ->
     it "opens the parent directory and creates an empty text editor", ->
-      runAtom [path.join(tempDirPath, "new-file")], {ATOM_HOME: AtomHome}, (client) ->
+      runAtom [path.join(tempDirPath, "new-file")], {ATOM_HOME: atomHome}, (client) ->
         client
           .waitForWindowCount(1, 1000)
           .waitForExist("atom-workspace", 5000)
@@ -36,13 +36,14 @@ describe "Starting Atom", ->
           .keys("Hello!")
           .execute -> atom.workspace.getActiveTextEditor().getText()
           .then ({value}) -> expect(value).toBe "Hello!"
+          .dispatchCommand("editor:delete-line")
 
   describe "when there is already a window open", ->
     it "reuses that window when opening files, but not when opening directories", ->
       tempFilePath = path.join(temp.mkdirSync("a-third-dir"), "a-file")
       fs.writeFileSync(tempFilePath, "This file was already here.")
 
-      runAtom [path.join(tempDirPath, "new-file")], {ATOM_HOME: AtomHome}, (client) ->
+      runAtom [path.join(tempDirPath, "new-file")], {ATOM_HOME: atomHome}, (client) ->
         client
           .waitForWindowCount(1, 1000)
           .waitForExist("atom-workspace", 5000)
@@ -50,7 +51,7 @@ describe "Starting Atom", ->
 
           # Opening another file reuses the same window and does not change the
           # project paths.
-          .startAnotherAtom([tempFilePath], ATOM_HOME: AtomHome)
+          .startAnotherAtom([tempFilePath], ATOM_HOME: atomHome)
           .waitForPaneItemCount(2, 5000)
           .waitForWindowCount(1, 1000)
           .treeViewRootDirectories()
@@ -60,7 +61,7 @@ describe "Starting Atom", ->
 
           # Opening another directory creates a second window.
           .waitForNewWindow(->
-            @startAnotherAtom([otherTempDirPath], ATOM_HOME: AtomHome)
+            @startAnotherAtom([otherTempDirPath], ATOM_HOME: atomHome)
           , 5000)
           .waitForExist("atom-workspace", 5000)
           .waitForPaneItemCount(0, 1000)
@@ -69,15 +70,14 @@ describe "Starting Atom", ->
 
   describe "reopening a directory that was previously opened", ->
     it "remembers the state of the window", ->
-      runAtom [tempDirPath], {ATOM_HOME: AtomHome}, (client) ->
+      runAtom [tempDirPath], {ATOM_HOME: atomHome}, (client) ->
         client
           .waitForExist("atom-workspace", 5000)
           .waitForPaneItemCount(0, 3000)
           .execute -> atom.workspace.open()
           .waitForPaneItemCount(1, 3000)
-          .execute -> atom.unloadEditorWindow()
 
-      runAtom [tempDirPath], {ATOM_HOME: AtomHome}, (client) ->
+      runAtom [tempDirPath], {ATOM_HOME: atomHome}, (client) ->
         client
           .waitForExist("atom-workspace", 5000)
           .waitForPaneItemCount(1, 5000)
@@ -87,7 +87,7 @@ describe "Starting Atom", ->
       nestedDir = path.join(otherTempDirPath, "nested-dir")
       fs.mkdirSync(nestedDir)
 
-      runAtom [tempDirPath, otherTempDirPath], {ATOM_HOME: AtomHome}, (client) ->
+      runAtom [tempDirPath, otherTempDirPath], {ATOM_HOME: atomHome}, (client) ->
         client
           .waitForExist("atom-workspace", 5000)
           .treeViewRootDirectories()
@@ -95,42 +95,67 @@ describe "Starting Atom", ->
 
           # Opening one of those directories again reuses the same window and
           # does not change the project paths.
-          .startAnotherAtom([nestedDir], ATOM_HOME: AtomHome)
+          .startAnotherAtom([nestedDir], ATOM_HOME: atomHome)
           .waitForExist("atom-workspace", 5000)
           .treeViewRootDirectories()
           .then ({value}) -> expect(value).toEqual([tempDirPath, otherTempDirPath])
 
   describe "when there is an existing window with no project path", ->
-    describe "opening a directory", ->
-      it "opens the directory in the existing window", ->
-        runAtom [], {ATOM_HOME: AtomHome}, (client) ->
-          client
-            .waitForExist("atom-workspace")
+    it "reuses that window to open a directory", ->
+      runAtom [], {ATOM_HOME: atomHome}, (client) ->
+        client
+          .waitForExist("atom-workspace")
+          .treeViewRootDirectories()
+          .then ({value}) -> expect(value).toEqual([])
+
+          .startAnotherAtom([tempDirPath], ATOM_HOME: atomHome)
+          .waitUntil(->
+            @treeViewRootDirectories()
+            .then ({value}) -> value[0] is tempDirPath
+          , 5000)
+          .then (result) -> expect(result).toBe(true)
+          .waitForWindowCount(1, 5000)
+
+  describe "launching with no path", ->
+    it "opens a new window with a single untitled buffer", ->
+      runAtom [], {ATOM_HOME: atomHome}, (client) ->
+        client
+          .waitForExist("atom-workspace")
+          .waitForPaneItemCount(1, 5000)
+
+          # Opening with no file paths always creates a new window, even if
+          # existing windows have no project paths.
+          .waitForNewWindow(->
+            @startAnotherAtom([], ATOM_HOME: atomHome)
+          , 5000)
+          .waitForExist("atom-workspace")
+          .waitForPaneItemCount(1, 5000)
+
+    it "reopens any previously opened windows", ->
+      runAtom [tempDirPath], {ATOM_HOME: atomHome}, (client) ->
+        client
+          .waitForExist("atom-workspace")
+          .waitForNewWindow(->
+            @startAnotherAtom([otherTempDirPath], ATOM_HOME: atomHome)
+          , 5000)
+          .waitForExist("atom-workspace")
+
+      runAtom [], {ATOM_HOME: atomHome}, (client) ->
+        windowProjectPaths = []
+
+        client
+          .waitForWindowCount(2, 10000)
+          .then ({value: windowHandles}) ->
+            @window(windowHandles[0])
             .treeViewRootDirectories()
-            .then ({value}) -> expect(value).toEqual([])
+            .then ({value: directories}) -> windowProjectPaths.push(directories)
 
-            .startAnotherAtom([tempDirPath], ATOM_HOME: AtomHome)
-            .waitUntil(->
-              @treeViewRootDirectories()
-              .then ({value}) -> value[0] is tempDirPath
-            , 5000)
-            .then (result) -> expect(result).toBe(true)
-            .waitForWindowCount(1, 5000)
+            .window(windowHandles[1])
+            .treeViewRootDirectories()
+            .then ({value: directories}) -> windowProjectPaths.push(directories)
 
-    describe "launching with no path", ->
-      it "always opens a new window with a single untitled buffer", ->
-        runAtom [], {ATOM_HOME: AtomHome}, (client) ->
-          client
-            .waitForExist("atom-workspace")
-            .waitForPaneItemCount(1, 5000)
-
-        runAtom [], {ATOM_HOME: AtomHome}, (client) ->
-          client
-            .waitForExist("atom-workspace")
-            .waitForPaneItemCount(1, 5000)
-
-            # Opening with no file paths always creates a new window, even if
-            # existing windows have no project paths.
-            .waitForNewWindow(->
-              @startAnotherAtom([], ATOM_HOME: AtomHome)
-            , 5000)
+            .call ->
+              expect(windowProjectPaths.sort()).toEqual [
+                [tempDirPath]
+                [otherTempDirPath]
+              ].sort()
diff --git a/spec/package-manager-spec.coffee b/spec/package-manager-spec.coffee
index db2a76135..8dcc6bc37 100644
--- a/spec/package-manager-spec.coffee
+++ b/spec/package-manager-spec.coffee
@@ -28,6 +28,12 @@ describe "PackageManager", ->
       expect(pack.metadata.name).toBe "package-with-invalid-styles"
       expect(pack.stylesheets.length).toBe 0
 
+      addErrorHandler = jasmine.createSpy()
+      atom.notifications.onDidAddNotification(addErrorHandler)
+      expect(-> pack.reloadStylesheets()).not.toThrow()
+      expect(addErrorHandler.callCount).toBe 2
+      expect(addErrorHandler.argsForCall[1][0].message).toContain("Failed to reload the package-with-invalid-styles package stylesheets")
+
     it "returns null if the package has an invalid package.json", ->
       addErrorHandler = jasmine.createSpy()
       atom.notifications.onDidAddNotification(addErrorHandler)
diff --git a/spec/pane-container-element-spec.coffee b/spec/pane-container-element-spec.coffee
new file mode 100644
index 000000000..0a5b11b39
--- /dev/null
+++ b/spec/pane-container-element-spec.coffee
@@ -0,0 +1,134 @@
+PaneContainer = require '../src/pane-container'
+PaneAxisElement = require '../src/pane-axis-element'
+PaneAxis = require '../src/pane-axis'
+
+describe "PaneContainerElement", ->
+  describe "when panes are added or removed", ->
+    [paneAxisElement, paneAxis] = []
+
+    beforeEach ->
+      paneAxis = new PaneAxis
+      paneAxisElement = new PaneAxisElement().initialize(paneAxis)
+
+    childTagNames = ->
+      child.nodeName.toLowerCase() for child in paneAxisElement.children
+
+    it "inserts or removes resize elements", ->
+      expect(childTagNames()).toEqual []
+
+      paneAxis.addChild(new PaneAxis)
+      expect(childTagNames()).toEqual [
+        'atom-pane-axis'
+      ]
+
+      paneAxis.addChild(new PaneAxis)
+      expect(childTagNames()).toEqual [
+        'atom-pane-axis'
+        'atom-pane-resize-handle'
+        'atom-pane-axis'
+      ]
+
+      paneAxis.addChild(new PaneAxis)
+      expect(childTagNames()).toEqual [
+        'atom-pane-axis'
+        'atom-pane-resize-handle'
+        'atom-pane-axis'
+        'atom-pane-resize-handle'
+        'atom-pane-axis'
+      ]
+
+      paneAxis.removeChild(paneAxis.getChildren()[2])
+      expect(childTagNames()).toEqual [
+        'atom-pane-axis'
+        'atom-pane-resize-handle'
+        'atom-pane-axis'
+      ]
+
+  describe "when the resize element is dragged ", ->
+    [container, containerElement] = []
+
+    beforeEach ->
+      container = new PaneContainer
+      containerElement = atom.views.getView(container)
+      document.querySelector('#jasmine-content').appendChild(containerElement)
+
+    dragElementToPosition = (element, clientX) ->
+      element.dispatchEvent(new MouseEvent('mousedown',
+        view: window
+        bubbles: true
+        button: 0
+      ))
+
+      element.dispatchEvent(new MouseEvent 'mousemove',
+        view: window
+        bubbles: true
+        clientX: clientX
+      )
+
+      element.dispatchEvent(new MouseEvent 'mouseup',
+        iew: window
+        bubbles: true
+        button: 0
+      )
+
+    getElementWidth = (element) ->
+      element.getBoundingClientRect().width
+
+    expectPaneScale = (pairs...) ->
+      for [pane, expectedFlexScale] in pairs
+        expect(pane.getFlexScale()).toBeCloseTo(expectedFlexScale, 0.1)
+
+    getResizeElement = (i) ->
+      containerElement.querySelectorAll('atom-pane-resize-handle')[i]
+
+    getPaneElement = (i) ->
+      containerElement.querySelectorAll('atom-pane')[i]
+
+    it "adds and removes panes in the direction that the pane is being dragged", ->
+      leftPane = container.getActivePane()
+      expectPaneScale [leftPane, 1]
+
+      middlePane = leftPane.splitRight()
+      expectPaneScale [leftPane, 1], [middlePane, 1]
+
+      dragElementToPosition(
+        getResizeElement(0),
+        getElementWidth(getPaneElement(0)) / 2
+      )
+      expectPaneScale [leftPane, 0.5], [middlePane, 1.5]
+
+      rightPane = middlePane.splitRight()
+      expectPaneScale [leftPane, 0.5], [middlePane, 1.5], [rightPane, 1]
+
+      dragElementToPosition(
+        getResizeElement(1),
+        getElementWidth(getPaneElement(0)) + getElementWidth(getPaneElement(1)) / 2
+      )
+      expectPaneScale [leftPane, 0.5], [middlePane, 0.75], [rightPane, 1.75]
+
+      middlePane.close()
+      expectPaneScale [leftPane, 0.44], [rightPane, 1.55]
+
+      leftPane.close()
+      expectPaneScale [rightPane, 1]
+
+    it "splits or closes panes in orthogonal direction that the pane is being dragged", ->
+      leftPane = container.getActivePane()
+      expectPaneScale [leftPane, 1]
+
+      rightPane = leftPane.splitRight()
+      expectPaneScale [leftPane, 1], [rightPane, 1]
+
+      dragElementToPosition(
+        getResizeElement(0),
+        getElementWidth(getPaneElement(0)) / 2
+      )
+      expectPaneScale [leftPane, 0.5], [rightPane, 1.5]
+
+      # dynamically split pane, pane's flexScale will become to 1
+      lowerPane = leftPane.splitDown()
+      expectPaneScale [lowerPane, 1], [leftPane, 1], [leftPane.getParent(), 0.5]
+
+      # dynamically close pane, the pane's flexscale will recorver to origin value
+      lowerPane.close()
+      expectPaneScale [leftPane, 0.5], [rightPane, 1.5]
diff --git a/spec/pane-spec.coffee b/spec/pane-spec.coffee
index ac6e1d26f..7d6410048 100644
--- a/spec/pane-spec.coffee
+++ b/spec/pane-spec.coffee
@@ -696,7 +696,10 @@ describe "Pane", ->
     pane = null
 
     beforeEach ->
-      pane = new Pane(items: [new Item("A", "a"), new Item("B", "b"), new Item("C", "c")])
+      params =
+        items: [new Item("A", "a"), new Item("B", "b"), new Item("C", "c")]
+        flexScale: 2
+      pane = new Pane(params)
 
     it "can serialize and deserialize the pane and all its items", ->
       newPane = pane.testSerialization()
diff --git a/spec/pane-view-spec.coffee b/spec/pane-view-spec.coffee
index 2df5aa68c..19fa247e0 100644
--- a/spec/pane-view-spec.coffee
+++ b/spec/pane-view-spec.coffee
@@ -118,6 +118,33 @@ describe "PaneView", ->
         paneModel.activateItem(view2)
         expect(pane.itemViews.find('#view-2').length).toBe 1
 
+    describe "when the new activeItem implements ::getPath", ->
+      beforeEach ->
+        paneModel.activateItem(editor1)
+
+      it "adds the file path as a data attribute to the pane", ->
+        expect(pane).toHaveAttr('data-active-item-path')
+
+      it "adds the file name as a data attribute to the pane", ->
+        expect(pane).toHaveAttr('data-active-item-name')
+
+      describe "when the activeItem is destroyed", ->
+        it "removes the data attributes", ->
+          pane.destroyItems()
+          expect(pane).not.toHaveAttr('data-active-item-path')
+          expect(pane).not.toHaveAttr('data-active-item-name')
+
+    describe "when the new activeItem does not implement ::getPath", ->
+      beforeEach ->
+        paneModel.activateItem(editor1)
+        paneModel.activateItem(document.createElement('div'))
+
+      it "does not add the file path as a data attribute to the pane", ->
+        expect(pane).not.toHaveAttr('data-active-item-path')
+
+      it "does not add the file name as data attribute to the pane", ->
+        expect(pane).not.toHaveAttr('data-active-item-name')
+
   describe "when an item is destroyed", ->
     it "triggers the 'pane:item-removed' event with the item and its former index", ->
       itemRemovedHandler = jasmine.createSpy("itemRemovedHandler")
@@ -333,3 +360,30 @@ describe "PaneView", ->
       pane3 = container3.getRoot()
       container3.attachToDom()
       expect(pane3).not.toMatchSelector(':has(:focus)')
+
+  describe "drag and drop", ->
+    buildDragEvent = (type, files) ->
+      dataTransfer =
+        files: files
+        data: {}
+        setData: (key, value) -> @data[key] = value
+        getData: (key) -> @data[key]
+
+      event = new CustomEvent("drop")
+      event.dataTransfer = dataTransfer
+      event
+
+    describe "when a file is dragged to window", ->
+      it "opens it", ->
+        spyOn(atom, "open")
+        event = buildDragEvent("drop", [ {path: "/fake1"}, {path: "/fake2"} ])
+        pane[0].dispatchEvent(event)
+        expect(atom.open.callCount).toBe 1
+        expect(atom.open.argsForCall[0][0]).toEqual pathsToOpen: ['/fake1', '/fake2']
+
+    describe "when a non-file is dragged to window", ->
+      it "does nothing", ->
+        spyOn(atom, "open")
+        event = buildDragEvent("drop", [])
+        pane[0].dispatchEvent(event)
+        expect(atom.open).not.toHaveBeenCalled()
diff --git a/spec/spec-helper.coffee b/spec/spec-helper.coffee
index d5d18b2ba..a0905ddf7 100644
--- a/spec/spec-helper.coffee
+++ b/spec/spec-helper.coffee
@@ -163,7 +163,6 @@ afterEach ->
 
   jasmine.unspy(atom, 'saveSync')
   ensureNoPathSubscriptions()
-  atom.grammars.clearObservers()
   waits(0) # yield to ui thread to make screen update more frequently
 
 ensureNoPathSubscriptions = ->
diff --git a/spec/theme-manager-spec.coffee b/spec/theme-manager-spec.coffee
index c39e4994b..98a85f389 100644
--- a/spec/theme-manager-spec.coffee
+++ b/spec/theme-manager-spec.coffee
@@ -390,6 +390,13 @@ describe "ThemeManager", ->
         expect(note.getType()).toBe 'error'
         expect(note.getMessage()).toContain 'Unable to watch path'
 
+    it "adds a notification when a theme's stylesheet is invalid", ->
+      addErrorHandler = jasmine.createSpy()
+      atom.notifications.onDidAddNotification(addErrorHandler)
+      expect(-> atom.packages.activatePackage('theme-with-invalid-styles')).not.toThrow()
+      expect(addErrorHandler.callCount).toBe 2
+      expect(addErrorHandler.argsForCall[1][0].message).toContain("Failed to activate the theme-with-invalid-styles theme")
+
   describe "when a non-existent theme is present in the config", ->
     beforeEach ->
       spyOn(console, 'warn')
diff --git a/spec/window-spec.coffee b/spec/window-spec.coffee
index 3c1a5b4ae..376a71ab3 100644
--- a/spec/window-spec.coffee
+++ b/spec/window-spec.coffee
@@ -141,33 +141,6 @@ describe "Window", ->
 
         expect(buffer.getSubscriptionCount()).toBe 0
 
-  describe "drag and drop", ->
-    buildDragEvent = (type, files) ->
-      dataTransfer =
-        files: files
-        data: {}
-        setData: (key, value) -> @data[key] = value
-        getData: (key) -> @data[key]
-
-      event = new CustomEvent("drop")
-      event.dataTransfer = dataTransfer
-      event
-
-    describe "when a file is dragged to window", ->
-      it "opens it", ->
-        spyOn(atom, "open")
-        event = buildDragEvent("drop", [ {path: "/fake1"}, {path: "/fake2"} ])
-        document.dispatchEvent(event)
-        expect(atom.open.callCount).toBe 1
-        expect(atom.open.argsForCall[0][0]).toEqual pathsToOpen: ['/fake1', '/fake2']
-
-    describe "when a non-file is dragged to window", ->
-      it "does nothing", ->
-        spyOn(atom, "open")
-        event = buildDragEvent("drop", [])
-        document.dispatchEvent(event)
-        expect(atom.open).not.toHaveBeenCalled()
-
   describe "when a link is clicked", ->
     it "opens the http/https links in an external application", ->
       shell = require 'shell'
diff --git a/src/atom.coffee b/src/atom.coffee
index 595dc7930..e2544640d 100644
--- a/src/atom.coffee
+++ b/src/atom.coffee
@@ -14,6 +14,7 @@ Model = require './model'
 {$} = require './space-pen-extensions'
 WindowEventHandler = require './window-event-handler'
 StylesElement = require './styles-element'
+StorageFolder = require './storage-folder'
 
 # Essential: Atom global for dealing with packages, themes, menus, and the window.
 #
@@ -73,34 +74,24 @@ class Atom extends Model
   # Loads and returns the serialized state corresponding to this window
   # if it exists; otherwise returns undefined.
   @loadState: (mode) ->
-    statePath = @getStatePath(@getLoadSettings().initialPaths, mode)
+    if stateKey = @getStateKey(@getLoadSettings().initialPaths, mode)
+      if state = @getStorageFolder().load(stateKey)
+        return state
 
-    if fs.existsSync(statePath)
+    if windowState = @getLoadSettings().windowState
       try
-        stateString = fs.readFileSync(statePath, 'utf8')
+        JSON.parse(@getLoadSettings().windowState)
       catch error
-        console.warn "Error reading window state: #{statePath}", error.stack, error
-    else
-      stateString = @getLoadSettings().windowState
-
-    try
-      JSON.parse(stateString) if stateString?
-    catch error
-      console.warn "Error parsing window state: #{statePath} #{error.stack}", error
+        console.warn "Error parsing window state: #{statePath} #{error.stack}", error
 
   # Returns the path where the state for the current window will be
   # located if it exists.
-  @getStatePath: (paths, mode) ->
-    switch mode
-      when 'spec'
-        filename = 'spec'
-      when 'editor'
-        if paths?.length > 0
-          sha1 = crypto.createHash('sha1').update(paths.slice().sort().join("\n")).digest('hex')
-          filename = "editor-#{sha1}"
-
-    if filename
-      path.join(@getStorageDirPath(), filename)
+  @getStateKey: (paths, mode) ->
+    if mode is 'spec'
+      'spec'
+    else if mode is 'editor' and paths?.length > 0
+      sha1 = crypto.createHash('sha1').update(paths.slice().sort().join("\n")).digest('hex')
+      "editor-#{sha1}"
     else
       null
 
@@ -110,11 +101,8 @@ class Atom extends Model
   @getConfigDirPath: ->
     @configDirPath ?= process.env.ATOM_HOME
 
-  # Get the path to Atom's storage directory.
-  #
-  # Returns the absolute path to ~/.atom/storage
-  @getStorageDirPath: ->
-    @storageDirPath ?= path.join(@getConfigDirPath(), 'storage')
+  @getStorageFolder: ->
+    @storageFolder ?= new StorageFolder(@getConfigDirPath())
 
   # Returns the load settings hash associated with the current window.
   @getLoadSettings: ->
@@ -227,7 +215,7 @@ class Atom extends Model
 
       if openDevTools
         @openDevTools()
-        @executeJavaScriptInDevTools('InspectorFrontendAPI.showConsole()')
+        @executeJavaScriptInDevTools('DevToolsAPI.showConsole()')
 
       @emit 'uncaught-error', arguments... if includeDeprecatedAPIs
       @emitter.emit 'did-throw-error', {message, url, line, column, originalError}
@@ -586,12 +574,12 @@ class Atom extends Model
 
   # Call this method when establishing a real application window.
   startEditorWindow: ->
-    {resourcePath, safeMode} = @getLoadSettings()
+    {safeMode} = @getLoadSettings()
 
     CommandInstaller = require './command-installer'
-    CommandInstaller.installAtomCommand resourcePath, false, (error) ->
+    CommandInstaller.installAtomCommand false, (error) ->
       console.warn error.message if error?
-    CommandInstaller.installApmCommand resourcePath, false, (error) ->
+    CommandInstaller.installApmCommand false, (error) ->
       console.warn error.message if error?
 
     dimensions = @restoreWindowDimensions()
@@ -791,11 +779,10 @@ class Atom extends Model
     dialog.showSaveDialog currentWindow, {title: 'Save File', defaultPath}
 
   saveSync: ->
-    stateString = JSON.stringify(@state)
-    if statePath = @constructor.getStatePath(@project?.getPaths(), @mode)
-      fs.writeFileSync(statePath, stateString, 'utf8')
+    if storageKey = @constructor.getStateKey(@project?.getPaths(), @mode)
+      @constructor.getStorageFolder().store(storageKey, @state)
     else
-      @getCurrentWindow().loadSettings.windowState = stateString
+      @getCurrentWindow().loadSettings.windowState = JSON.stringify(@state)
 
   crashMainProcess: ->
     remote.process.crash()
diff --git a/src/browser/atom-application.coffee b/src/browser/atom-application.coffee
index 2fee79f0b..dbe29caab 100644
--- a/src/browser/atom-application.coffee
+++ b/src/browser/atom-application.coffee
@@ -3,6 +3,7 @@ ApplicationMenu = require './application-menu'
 AtomProtocolHandler = require './atom-protocol-handler'
 AutoUpdateManager = require './auto-update-manager'
 BrowserWindow = require 'browser-window'
+StorageFolder = require '../storage-folder'
 Menu = require 'menu'
 app = require 'app'
 fs = require 'fs-plus'
@@ -43,7 +44,6 @@ class AtomApplication
       createAtomApplication()
       return
 
-
     client = net.connect {path: options.socketPath}, ->
       client.write JSON.stringify(options), ->
         client.end()
@@ -78,10 +78,13 @@ class AtomApplication
     @listenForArgumentsFromNewProcess()
     @setupJavaScriptArguments()
     @handleEvents()
+    @storageFolder = new StorageFolder(process.env.ATOM_HOME)
 
-    @openWithOptions(options)
+    if options.pathsToOpen?.length > 0 or options.urlsToOpen?.length > 0 or options.test
+      @openWithOptions(options)
+    else
+      @loadState() or @openPath(options)
 
-  # Opens a new window based on the options provided.
   openWithOptions: ({pathsToOpen, urlsToOpen, test, pidToKillWhenClosed, devMode, safeMode, apiPreviewMode, newWindow, specDirectory, logFile}) ->
     if test
       @runSpecs({exitWhenDone: true, @resourcePath, specDirectory, logFile})
@@ -193,11 +196,14 @@ class AtomApplication
     @openPathOnEvent('application:open-your-keymap', 'atom://.atom/keymap')
     @openPathOnEvent('application:open-your-snippets', 'atom://.atom/snippets')
     @openPathOnEvent('application:open-your-stylesheet', 'atom://.atom/stylesheet')
-    @openPathOnEvent('application:open-license', path.join(@resourcePath, 'LICENSE.md'))
+    @openPathOnEvent('application:open-license', path.join(process.resourcesPath, 'LICENSE.md'))
 
     app.on 'window-all-closed', ->
       app.quit() if process.platform in ['win32', 'linux']
 
+    app.on 'before-quit', =>
+      @saveState()
+
     app.on 'will-quit', =>
       @killAllProcesses()
       @deleteSocketFile()
@@ -328,7 +334,7 @@ class AtomApplication
   focusedWindow: ->
     _.find @windows, (atomWindow) -> atomWindow.isFocused()
 
-  # Public: Opens multiple paths, in existing windows if possible.
+  # Public: Opens a single path, in an existing window if possible.
   #
   # options -
   #   :pathToOpen - The file path to open
@@ -341,7 +347,7 @@ class AtomApplication
   openPath: ({pathToOpen, pidToKillWhenClosed, newWindow, devMode, safeMode, apiPreviewMode, window}) ->
     @openPaths({pathsToOpen: [pathToOpen], pidToKillWhenClosed, newWindow, devMode, safeMode, apiPreviewMode, window})
 
-  # Public: Opens a single path, in an existing window if possible.
+  # Public: Opens multiple paths, in existing windows if possible.
   #
   # options -
   #   :pathsToOpen - The array of file paths to open
@@ -411,6 +417,33 @@ class AtomApplication
         console.log("Killing process #{pid} failed: #{error.code ? error.message}")
     delete @pidsToOpenWindows[pid]
 
+  saveState: ->
+    states = []
+    for window in @windows
+      if loadSettings = window.getLoadSettings()
+        unless loadSettings.isSpec
+          states.push(_.pick(loadSettings,
+            'initialPaths'
+            'devMode'
+            'safeMode'
+            'apiPreviewMode'
+          ))
+    @storageFolder.store('application.json', states)
+
+  loadState: ->
+    if (states = @storageFolder.load('application.json'))?.length > 0
+      for state in states
+        @openWithOptions({
+          pathsToOpen: state.initialPaths
+          urlsToOpen: []
+          devMode: state.devMode
+          safeMode: state.safeMode
+          apiPreviewMode: state.apiPreviewMode
+        })
+      true
+    else
+      false
+
   # Open an atom:// url.
   #
   # The host of the URL being opened is assumed to be the package name
diff --git a/src/browser/atom-window.coffee b/src/browser/atom-window.coffee
index fff98799c..6a6abb4b9 100644
--- a/src/browser/atom-window.coffee
+++ b/src/browser/atom-window.coffee
@@ -87,8 +87,9 @@ class AtomWindow
       hash: encodeURIComponent(JSON.stringify(loadSettings))
 
   getLoadSettings: ->
-    hash = url.parse(@browserWindow.webContents.getUrl()).hash.substr(1)
-    JSON.parse(decodeURIComponent(hash))
+    if @browserWindow.webContents.loaded
+      hash = url.parse(@browserWindow.webContents.getUrl()).hash.substr(1)
+      JSON.parse(decodeURIComponent(hash))
 
   hasProjectPath: -> @getLoadSettings().initialPaths?.length > 0
 
@@ -105,7 +106,7 @@ class AtomWindow
     true
 
   containsPath: (pathToCheck) ->
-    @getLoadSettings().initialPaths?.some (projectPath) ->
+    @getLoadSettings()?.initialPaths?.some (projectPath) ->
       if not projectPath
         false
       else if not pathToCheck
diff --git a/src/command-installer.coffee b/src/command-installer.coffee
index c0ed22482..afd5000c1 100644
--- a/src/command-installer.coffee
+++ b/src/command-installer.coffee
@@ -1,6 +1,4 @@
 path = require 'path'
-_ = require 'underscore-plus'
-async = require 'async'
 fs = require 'fs-plus'
 runas = null # defer until used
 
@@ -36,12 +34,11 @@ module.exports =
         message: "Failed to install shell commands"
         detailedMessage: error.message
 
-    resourcePath = atom.getLoadSettings().resourcePath
-    @installAtomCommand resourcePath, true, (error) =>
+    @installAtomCommand true, (error) =>
       if error?
         showErrorDialog(error)
       else
-        @installApmCommand resourcePath, true, (error) ->
+        @installApmCommand true, (error) ->
           if error?
             showErrorDialog(error)
           else
@@ -49,12 +46,12 @@ module.exports =
               message: "Commands installed."
               detailedMessage: "The shell commands `atom` and `apm` are installed."
 
-  installAtomCommand: (resourcePath, askForPrivilege, callback) ->
-    commandPath = path.join(resourcePath, 'atom.sh')
+  installAtomCommand: (askForPrivilege, callback) ->
+    commandPath = path.join(process.resourcesPath, 'app', 'atom.sh')
     @createSymlink commandPath, askForPrivilege, callback
 
-  installApmCommand: (resourcePath, askForPrivilege, callback) ->
-    commandPath = path.join(resourcePath, 'apm', 'node_modules', '.bin', 'apm')
+  installApmCommand: (askForPrivilege, callback) ->
+    commandPath = path.join(process.resourcesPath, 'app', 'apm', 'node_modules', '.bin', 'apm')
     @createSymlink commandPath, askForPrivilege, callback
 
   createSymlink: (commandPath, askForPrivilege, callback) ->
diff --git a/src/package-manager.coffee b/src/package-manager.coffee
index 386a65e68..8527188d3 100644
--- a/src/package-manager.coffee
+++ b/src/package-manager.coffee
@@ -111,7 +111,7 @@ class PackageManager
 
     commandName = 'apm'
     commandName += '.cmd' if process.platform is 'win32'
-    apmRoot = path.resolve(__dirname, '..', 'apm')
+    apmRoot = path.join(process.resourcesPath, 'app', 'apm')
     @apmPath = path.join(apmRoot, 'bin', commandName)
     unless fs.isFileSync(@apmPath)
       @apmPath = path.join(apmRoot, 'node_modules', 'atom-package-manager', 'bin', commandName)
diff --git a/src/package.coffee b/src/package.coffee
index 74c4f0eb8..de90c6cb4 100644
--- a/src/package.coffee
+++ b/src/package.coffee
@@ -371,7 +371,12 @@ class Package
 
   reloadStylesheets: ->
     oldSheets = _.clone(@stylesheets)
-    @loadStylesheets()
+
+    try
+      @loadStylesheets()
+    catch error
+      @handleError("Failed to reload the #{@name} package stylesheets", error)
+
     @stylesheetDisposables?.dispose()
     @stylesheetDisposables = new CompositeDisposable
     @stylesheetsActivated = false
diff --git a/src/pane-axis-element.coffee b/src/pane-axis-element.coffee
index 569c36534..f9dd15697 100644
--- a/src/pane-axis-element.coffee
+++ b/src/pane-axis-element.coffee
@@ -1,5 +1,6 @@
 {CompositeDisposable} = require 'event-kit'
 {callAttachHooks} = require './space-pen-extensions'
+PaneResizeHandleElement = require './pane-resize-handle-element'
 
 class PaneAxisElement extends HTMLElement
   createdCallback: ->
@@ -12,6 +13,7 @@ class PaneAxisElement extends HTMLElement
     @subscriptions.add @model.onDidAddChild(@childAdded.bind(this))
     @subscriptions.add @model.onDidRemoveChild(@childRemoved.bind(this))
     @subscriptions.add @model.onDidReplaceChild(@childReplaced.bind(this))
+    @subscriptions.add @model.observeFlexScale(@flexScaleChanged.bind(this))
 
     @childAdded({child, index}) for child, index in @model.getChildren()
 
@@ -22,13 +24,33 @@ class PaneAxisElement extends HTMLElement
         @classList.add('vertical', 'pane-column')
     this
 
+  isPaneResizeHandleElement: (element) ->
+    element?.nodeName.toLowerCase() is 'atom-pane-resize-handle'
+
   childAdded: ({child, index}) ->
     view = atom.views.getView(child)
-    @insertBefore(view, @children[index])
+    @insertBefore(view, @children[index * 2])
+
+    prevElement = view.previousSibling
+    # if previous element is not pane resize element, then insert new resize element
+    if prevElement? and not @isPaneResizeHandleElement(prevElement)
+      resizeHandle = document.createElement('atom-pane-resize-handle')
+      @insertBefore(resizeHandle, view)
+
+    nextElement = view.nextSibling
+    # if next element isnot resize element, then insert new resize element
+    if nextElement? and not @isPaneResizeHandleElement(nextElement)
+      resizeHandle = document.createElement('atom-pane-resize-handle')
+      @insertBefore(resizeHandle, nextElement)
+
     callAttachHooks(view) # for backward compatibility with SpacePen views
 
   childRemoved: ({child}) ->
     view = atom.views.getView(child)
+    siblingView = view.previousSibling
+    # make sure next sibling view is pane resize view
+    if siblingView? and @isPaneResizeHandleElement(siblingView)
+      siblingView.remove()
     view.remove()
 
   childReplaced: ({index, oldChild, newChild}) ->
@@ -37,6 +59,8 @@ class PaneAxisElement extends HTMLElement
     @childAdded({child: newChild, index})
     focusedElement?.focus() if document.activeElement is document.body
 
+  flexScaleChanged: (flexScale) -> @style.flexGrow = flexScale
+
   hasFocus: ->
     this is document.activeElement or @contains(document.activeElement)
 
diff --git a/src/pane-axis.coffee b/src/pane-axis.coffee
index ec77b17d2..1fba48d37 100644
--- a/src/pane-axis.coffee
+++ b/src/pane-axis.coffee
@@ -12,13 +12,14 @@ class PaneAxis extends Model
   container: null
   orientation: null
 
-  constructor: ({@container, @orientation, children}) ->
+  constructor: ({@container, @orientation, children, flexScale}={}) ->
     @emitter = new Emitter
     @subscriptionsByChild = new WeakMap
     @subscriptions = new CompositeDisposable
     @children = []
     if children?
       @addChild(child) for child in children
+    @flexScale = flexScale ? 1
 
   deserializeParams: (params) ->
     {container} = params
@@ -28,6 +29,13 @@ class PaneAxis extends Model
   serializeParams: ->
     children: @children.map (child) -> child.serialize()
     orientation: @orientation
+    flexScale: @flexScale
+
+  getFlexScale: -> @flexScale
+
+  setFlexScale: (@flexScale) ->
+    @emitter.emit 'did-change-flex-scale', @flexScale
+    @flexScale
 
   getParent: -> @parent
 
@@ -59,6 +67,13 @@ class PaneAxis extends Model
   onDidDestroy: (fn) ->
     @emitter.on 'did-destroy', fn
 
+  onDidChangeFlexScale: (fn) ->
+    @emitter.on 'did-change-flex-scale', fn
+
+  observeFlexScale: (fn) ->
+    fn(@flexScale)
+    @onDidChangeFlexScale(fn)
+
   addChild: (child, index=@children.length) ->
     child.setParent(this)
     child.setContainer(@container)
@@ -68,6 +83,16 @@ class PaneAxis extends Model
     @children.splice(index, 0, child)
     @emitter.emit 'did-add-child', {child, index}
 
+  adjustFlexScale: ->
+    # get current total flex scale of children
+    total = 0
+    total += child.getFlexScale() for child in @children
+
+    needTotal = @children.length
+    # set every child's flex scale by the ratio
+    for child in @children
+      child.setFlexScale(needTotal * child.getFlexScale() / total)
+
   removeChild: (child, replacing=false) ->
     index = @children.indexOf(child)
     throw new Error("Removing non-existent child") if index is -1
@@ -75,6 +100,7 @@ class PaneAxis extends Model
     @unsubscribeFromChild(child)
 
     @children.splice(index, 1)
+    @adjustFlexScale()
     @emitter.emit 'did-remove-child', {child, index}
     @reparentLastChild() if not replacing and @children.length < 2
 
@@ -98,7 +124,9 @@ class PaneAxis extends Model
     @addChild(newChild, index + 1)
 
   reparentLastChild: ->
-    @parent.replaceChild(this, @children[0])
+    lastChild = @children[0]
+    lastChild.setFlexScale(@flexScale)
+    @parent.replaceChild(this, lastChild)
     @destroy()
 
   subscribeToChild: (child) ->
diff --git a/src/pane-element.coffee b/src/pane-element.coffee
index f5bfc18bd..15990bcc2 100644
--- a/src/pane-element.coffee
+++ b/src/pane-element.coffee
@@ -1,3 +1,4 @@
+path = require 'path'
 {CompositeDisposable} = require 'event-kit'
 Grim = require 'grim'
 {$, callAttachHooks, callRemoveHooks} = require './space-pen-extensions'
@@ -38,8 +39,21 @@ class PaneElement extends HTMLElement
     handleBlur = (event) =>
       @model.blur() unless @contains(event.relatedTarget)
 
+    handleDragOver = (event) ->
+      event.preventDefault()
+      event.stopPropagation()
+
+    handleDrop = (event) =>
+      event.preventDefault()
+      event.stopPropagation()
+      @getModel().activate()
+      pathsToOpen = Array::map.call event.dataTransfer.files, (file) -> file.path
+      atom.open({pathsToOpen}) if pathsToOpen.length > 0
+
     @addEventListener 'focus', handleFocus, true
     @addEventListener 'blur', handleBlur, true
+    @addEventListener 'dragover', handleDragOver
+    @addEventListener 'drop', handleDrop
 
   createSpacePenShim: ->
     PaneView ?= require './pane-view'
@@ -51,6 +65,8 @@ class PaneElement extends HTMLElement
     @subscriptions.add @model.observeActiveItem(@activeItemChanged.bind(this))
     @subscriptions.add @model.onDidRemoveItem(@itemRemoved.bind(this))
     @subscriptions.add @model.onDidDestroy(@paneDestroyed.bind(this))
+    @subscriptions.add @model.observeFlexScale(@flexScaleChanged.bind(this))
+
     @__spacePenView.setModel(@model) if Grim.includeDeprecatedAPIs
     this
 
@@ -66,11 +82,18 @@ class PaneElement extends HTMLElement
       @classList.remove('active')
 
   activeItemChanged: (item) ->
+    delete @dataset.activeItemName
+    delete @dataset.activeItemPath
+
     return unless item?
 
     hasFocus = @hasFocus()
     itemView = atom.views.getView(item)
 
+    if itemPath = item.getPath?()
+      @dataset.activeItemName = path.basename(itemPath)
+      @dataset.activeItemPath = itemPath
+
     unless @itemViews.contains(itemView)
       @itemViews.appendChild(itemView)
       callAttachHooks(itemView)
@@ -104,6 +127,9 @@ class PaneElement extends HTMLElement
   paneDestroyed: ->
     @subscriptions.dispose()
 
+  flexScaleChanged: (flexScale) ->
+    @style.flexGrow = flexScale
+
   getActiveView: -> atom.views.getView(@model.getActiveItem())
 
   hasFocus: ->
diff --git a/src/pane-resize-handle-element.coffee b/src/pane-resize-handle-element.coffee
new file mode 100644
index 000000000..47548bc60
--- /dev/null
+++ b/src/pane-resize-handle-element.coffee
@@ -0,0 +1,64 @@
+class PaneResizeHandleElement extends HTMLElement
+  createdCallback: ->
+    @resizePane = @resizePane.bind(this)
+    @resizeStopped = @resizeStopped.bind(this)
+    @subscribeToDOMEvents()
+
+  subscribeToDOMEvents: ->
+    @addEventListener 'dblclick', @resizeToFitContent.bind(this)
+    @addEventListener 'mousedown', @resizeStarted.bind(this)
+
+  attachedCallback: ->
+    @isHorizontal = @parentElement.classList.contains("horizontal")
+    @classList.add if @isHorizontal then 'horizontal' else 'vertical'
+
+  resizeToFitContent: ->
+    # clear flex-grow css style of both pane
+    @previousSibling.model.setFlexScale(1)
+    @nextSibling.model.setFlexScale(1)
+
+  resizeStarted: (e) ->
+    e.stopPropagation()
+    document.addEventListener 'mousemove', @resizePane
+    document.addEventListener 'mouseup', @resizeStopped
+
+  resizeStopped: ->
+    document.removeEventListener 'mousemove', @resizePane
+    document.removeEventListener 'mouseup', @resizeStopped
+
+  calcRatio: (ratio1, ratio2, total) ->
+    allRatio = ratio1 + ratio2
+    [total * ratio1 / allRatio, total * ratio2 / allRatio]
+
+  setFlexGrow: (prevSize, nextSize) ->
+    @prevModel = @previousSibling.model
+    @nextModel = @nextSibling.model
+    totalScale = @prevModel.getFlexScale() + @nextModel.getFlexScale()
+    flexGrows = @calcRatio(prevSize, nextSize, totalScale)
+    @prevModel.setFlexScale flexGrows[0]
+    @nextModel.setFlexScale flexGrows[1]
+
+  fixInRange: (val, minValue, maxValue) ->
+    Math.min(Math.max(val, minValue), maxValue)
+
+  resizePane: ({clientX, clientY, which}) ->
+    return @resizeStopped() unless which is 1
+
+    if @isHorizontal
+      totalWidth = @previousSibling.clientWidth + @nextSibling.clientWidth
+      #get the left and right width after move the resize view
+      leftWidth = clientX - @previousSibling.getBoundingClientRect().left
+      leftWidth = @fixInRange(leftWidth, 0, totalWidth)
+      rightWidth = totalWidth - leftWidth
+      # set the flex grow by the ratio of left width and right width
+      # to change pane width
+      @setFlexGrow(leftWidth, rightWidth)
+    else
+      totalHeight = @previousSibling.clientHeight + @nextSibling.clientHeight
+      topHeight = clientY - @previousSibling.getBoundingClientRect().top
+      topHeight = @fixInRange(topHeight, 0, totalHeight)
+      bottomHeight = totalHeight - topHeight
+      @setFlexGrow(topHeight, bottomHeight)
+
+module.exports = PaneResizeHandleElement =
+document.registerElement 'atom-pane-resize-handle', prototype: PaneResizeHandleElement.prototype
diff --git a/src/pane.coffee b/src/pane.coffee
index 0d8c68066..38c8d9201 100644
--- a/src/pane.coffee
+++ b/src/pane.coffee
@@ -28,6 +28,7 @@ class Pane extends Model
 
     @addItems(compact(params?.items ? []))
     @setActiveItem(@items[0]) unless @getActiveItem()?
+    @setFlexScale(params?.flexScale ? 1)
 
   # Called by the Serializable mixin during serialization.
   serializeParams: ->
@@ -40,6 +41,7 @@ class Pane extends Model
     items: compact(@items.map((item) -> item.serialize?()))
     activeItemURI: activeItemURI
     focused: @focused
+    flexScale: @flexScale
 
   # Called by the Serializable mixin during deserialization.
   deserializeParams: (params) ->
@@ -66,10 +68,36 @@ class Pane extends Model
       @container = container
       container.didAddPane({pane: this})
 
+  setFlexScale: (@flexScale) ->
+    @emitter.emit 'did-change-flex-scale', @flexScale
+    @flexScale
+
+  getFlexScale: -> @flexScale
   ###
   Section: Event Subscription
   ###
 
+  # Public: Invoke the given callback when the pane resize
+  #
+  # the callback will be invoked when pane's flexScale property changes
+  #
+  # * `callback` {Function} to be called when the pane is resized
+  #
+  # Returns a {Disposable} on which '.dispose()' can be called to unsubscribe.
+  onDidChangeFlexScale: (callback) ->
+    @emitter.on 'did-change-flex-scale', callback
+
+  # Public: Invoke the given callback with all current and future items.
+  #
+  # * `callback` {Function} to be called with current and future items.
+  #   * `item` An item that is present in {::getItems} at the time of
+  #     subscription or that is added at some later time.
+  #
+  # Returns a {Disposable} on which `.dispose()` can be called to unsubscribe.
+  observeFlexScale: (callback) ->
+    callback(@flexScale)
+    @onDidChangeFlexScale(callback)
+
   # Public: Invoke the given callback when the pane is activated.
   #
   # The given callback will be invoked whenever {::activate} is called on the
@@ -591,7 +619,8 @@ class Pane extends Model
       params.items.push(@copyActiveItem())
 
     if @parent.orientation isnt orientation
-      @parent.replaceChild(this, new PaneAxis({@container, orientation, children: [this]}))
+      @parent.replaceChild(this, new PaneAxis({@container, orientation, children: [this], @flexScale}))
+      @setFlexScale(1)
 
     newPane = new @constructor(params)
     switch side
diff --git a/src/storage-folder.coffee b/src/storage-folder.coffee
new file mode 100644
index 000000000..bf969dee2
--- /dev/null
+++ b/src/storage-folder.coffee
@@ -0,0 +1,27 @@
+path = require "path"
+fs = require "fs-plus"
+
+module.exports =
+class StorageFolder
+  constructor: (containingPath) ->
+    @path = path.join(containingPath, "storage")
+
+  store: (name, object) ->
+    fs.writeFileSync(@pathForKey(name), JSON.stringify(object), 'utf8')
+
+  load: (name) ->
+    statePath = @pathForKey(name)
+    try
+      stateString = fs.readFileSync(statePath, 'utf8')
+    catch error
+      unless error.code is 'ENOENT'
+        console.warn "Error reading state file: #{statePath}", error.stack, error
+      return undefined
+
+    try
+      JSON.parse(stateString)
+    catch error
+      console.warn "Error parsing state file: #{statePath}", error.stack, error
+
+  pathForKey: (name) -> path.join(@getPath(), name)
+  getPath: -> @path
diff --git a/src/task.coffee b/src/task.coffee
index 9572494b8..d752ea11d 100644
--- a/src/task.coffee
+++ b/src/task.coffee
@@ -83,7 +83,7 @@ class Task
     taskPath = taskPath.replace(/\\/g, "\\\\")
 
     env = _.extend({}, process.env, {taskPath, userAgent: navigator.userAgent})
-    @childProcess = fork '--eval', [bootstrap], {env, cwd: __dirname}
+    @childProcess = fork '--eval', [bootstrap], {env, silent: true}
 
     @on "task:log", -> console.log(arguments...)
     @on "task:warn", -> console.warn(arguments...)
@@ -100,6 +100,11 @@ class Task
     @childProcess.removeAllListeners()
     @childProcess.on 'message', ({event, args}) =>
       @emit(event, args...) if @childProcess?
+    # Catch the errors that happened before task-bootstrap.
+    @childProcess.stdout.on 'data', (data) ->
+      console.log data.toString()
+    @childProcess.stderr.on 'data', (data) ->
+      console.error data.toString()
 
   # Public: Starts the task.
   #
diff --git a/src/theme-package.coffee b/src/theme-package.coffee
index e1b87e783..f14750d2f 100644
--- a/src/theme-package.coffee
+++ b/src/theme-package.coffee
@@ -14,11 +14,7 @@ class ThemePackage extends Package
     atom.config.removeAtKeyPath('core.themes', @name)
 
   load: ->
-    @measure 'loadTime', =>
-      try
-        @metadata ?= Package.loadMetadata(@path)
-      catch error
-        console.warn "Failed to load theme named '#{@name}'", error.stack ? error
+    @loadTime = 0
     this
 
   activate: ->
@@ -26,7 +22,10 @@ class ThemePackage extends Package
 
     @activationDeferred = Q.defer()
     @measure 'activateTime', =>
-      @loadStylesheets()
-      @activateNow()
+      try
+        @loadStylesheets()
+        @activateNow()
+      catch error
+        @handleError("Failed to activate the #{@name} theme", error)
 
     @activationDeferred.promise
diff --git a/src/window-event-handler.coffee b/src/window-event-handler.coffee
index 96518c446..7d67e87ab 100644
--- a/src/window-event-handler.coffee
+++ b/src/window-event-handler.coffee
@@ -1,6 +1,5 @@
 path = require 'path'
 {$} = require './space-pen-extensions'
-_ = require 'underscore-plus'
 {Disposable} = require 'event-kit'
 ipc = require 'ipc'
 shell = require 'shell'
@@ -136,12 +135,11 @@ class WindowEventHandler
   onDrop: (event) ->
     event.preventDefault()
     event.stopPropagation()
-    pathsToOpen = _.pluck(event.dataTransfer.files, 'path')
-    atom.open({pathsToOpen}) if pathsToOpen.length > 0
 
   onDragOver: (event) ->
     event.preventDefault()
     event.stopPropagation()
+    event.dataTransfer.dropEffect = 'none'
 
   openLink: ({target, currentTarget}) ->
     location = target?.getAttribute('href') or currentTarget?.getAttribute('href')
diff --git a/static/panes.less b/static/panes.less
index bf275e6da..163721fcc 100644
--- a/static/panes.less
+++ b/static/panes.less
@@ -4,19 +4,42 @@
 // settings-view, the archive-view, the image-view. Etc. Basically a non-
 // editor resource with a tab.
 atom-pane-container {
+  position: relative;
   display: -webkit-flex;
   -webkit-flex: 1;
 
-  atom-pane-axis.vertical {
+  atom-pane-axis {
     display: -webkit-flex;
     -webkit-flex: 1;
+
+    & > atom-pane-resize-handle {
+      position: absolute;
+      z-index: 3;
+    }
+  }
+
+  atom-pane-axis.vertical {
     -webkit-flex-direction: column;
+
+    & > atom-pane-resize-handle {
+      width: 100%;
+      height: 8px;
+      margin-top: -4px;
+      cursor: ns-resize;
+      border-bottom: none;
+    }
   }
 
   atom-pane-axis.horizontal {
-    display: -webkit-flex;
-    -webkit-flex: 1;
     -webkit-flex-direction: row;
+
+    & > atom-pane-resize-handle {
+      width: 8px;
+      height: 100%;
+      margin-left: -4px;
+      cursor: ew-resize;
+      border-right: none;
+    }
   }
 
   atom-pane {