diff --git a/spec/spec-helper.coffee b/spec/spec-helper.coffee
index a902fc2b4..db907b685 100644
--- a/spec/spec-helper.coffee
+++ b/spec/spec-helper.coffee
@@ -18,6 +18,7 @@ atom.themes.loadBaseStylesheets()
 atom.themes.requireStylesheet '../static/jasmine'
 
 fixturePackagesPath = path.resolve(__dirname, './fixtures/packages')
+atom.packages.packageDirPaths.unshift(fixturePackagesPath)
 atom.keymap.loadBundledKeymaps()
 [bindingSetsToRestore, bindingSetsByFirstKeystrokeToRestore] = []
 
@@ -50,7 +51,9 @@ beforeEach ->
   bindingSetsByFirstKeystrokeToRestore = _.clone(keymap.bindingSetsByFirstKeystroke)
 
   # reset config before each spec; don't load or save from/to `config.json`
-  config = new Config()
+  config = new Config
+    resourcePath: window.resourcePath
+    configDirPath: atom.getConfigDirPath()
   config.packageDirPaths.unshift(fixturePackagesPath)
   spyOn(config, 'load')
   spyOn(config, 'save')
diff --git a/src/atom-application.coffee b/src/atom-application.coffee
index b54b99bfa..2d3bb244f 100644
--- a/src/atom-application.coffee
+++ b/src/atom-application.coffee
@@ -51,7 +51,7 @@ class AtomApplication
   version: null
 
   constructor: (options) ->
-    {@resourcePath, @version} = options
+    {@resourcePath, @version, @devMode} = options
     global.atomApplication = this
 
     @pidsToOpenWindows = {}
@@ -147,7 +147,7 @@ class AtomApplication
 
     app.on 'open-url', (event, urlToOpen) =>
       event.preventDefault()
-      @openUrl(urlToOpen)
+      @openUrl({urlToOpen, @devMode})
 
     autoUpdater.on 'ready-for-update-on-quit', (event, version, quitAndUpdateCallback) =>
       event.preventDefault()
@@ -251,9 +251,11 @@ class AtomApplication
             console.log("Killing process #{pid} failed: #{error.code}")
         delete @pidsToOpenWindows[pid]
 
-  # Private: Handles an atom:// url.
+  # Private: Open an atom:// url.
   #
-  # Currently only supports atom://session/<session-id> urls.
+  # The host of the URL being opened is assumed to be the package name
+  # responsible for opening the URL.  A new window will be created with
+  # that package's `urlMain` as the bootstrap script.
   #
   # * options
   #    + urlToOpen:
@@ -261,15 +263,25 @@ class AtomApplication
   #    + devMode:
   #      Boolean to control the opened window's dev mode.
   openUrl: ({urlToOpen, devMode}) ->
-    parsedUrl = url.parse(urlToOpen)
-    if parsedUrl.host is 'session'
-      sessionId = parsedUrl.path.split('/')[1]
-      console.log "Joining session #{sessionId}"
-      if sessionId
-        bootstrapScript = 'collaboration/lib/bootstrap'
-        new AtomWindow({bootstrapScript, @resourcePath, sessionId, devMode})
+    unless @packages?
+      PackageManager = require './package-manager'
+      fsUtils = require './fs-utils'
+      @packages = new PackageManager
+        configDirPath: fsUtils.absolute('~/.atom')
+        devMode: devMode
+        resourcePath: @resourcePath
+
+    packageName = url.parse(urlToOpen).host
+    pack = _.find @packages.getAvailablePackageMetadata(), ({name}) -> name is packageName
+    if pack?
+      if pack.urlMain
+        packagePath = @packages.resolvePackagePath(packageName)
+        bootstrapScript = path.resolve(packagePath, pack.urlMain)
+        new AtomWindow({bootstrapScript, @resourcePath, devMode, urlToOpen})
+      else
+        console.log "Package '#{pack.name}' does not have a url main: #{urlToOpen}"
     else
-      console.log "Opening unknown url #{urlToOpen}"
+      console.log "Opening unknown url: #{urlToOpen}"
 
   # Private: Opens up a new {AtomWindow} to run specs within.
   #
diff --git a/src/atom.coffee b/src/atom.coffee
index 07569171e..f4ce8e441 100644
--- a/src/atom.coffee
+++ b/src/atom.coffee
@@ -27,6 +27,9 @@ class Atom
   initialize: ->
     @unsubscribe()
 
+    {devMode, resourcePath} = atom.getLoadSettings()
+    configDirPath = @getConfigDirPath()
+
     Config = require './config'
     Keymap = require './keymap'
     PackageManager = require './package-manager'
@@ -35,7 +38,7 @@ class Atom
     ThemeManager = require './theme-manager'
     ContextMenuManager = require './context-menu-manager'
 
-    @packages = new PackageManager()
+    @packages = new PackageManager({devMode, configDirPath, resourcePath})
 
     #TODO Remove once packages have been updated to not touch atom.packageStates directly
     @__defineGetter__ 'packageStates', => @packages.packageStates
@@ -43,8 +46,8 @@ class Atom
 
     @subscribe @packages, 'loaded', => @watchThemes()
     @themes = new ThemeManager()
-    @contextMenu = new ContextMenuManager(@getLoadSettings().devMode)
-    @config = new Config()
+    @contextMenu = new ContextMenuManager(devMode)
+    @config = new Config({configDirPath, resourcePath})
     @pasteboard = new Pasteboard()
     @keymap = new Keymap()
     @syntax = deserialize(@getWindowState('syntax')) ? new Syntax()
@@ -213,6 +216,10 @@ class Atom
   getHomeDirPath: ->
     app.getHomeDir()
 
+  # Public: Get the directory path to Atom's configuration area.
+  getConfigDirPath: ->
+    @configDirPath ?= fsUtils.absolute('~/.atom')
+
   getWindowStatePath: ->
     switch @windowMode
       when 'spec'
diff --git a/src/config.coffee b/src/config.coffee
index 1b2466381..f6104747f 100644
--- a/src/config.coffee
+++ b/src/config.coffee
@@ -7,8 +7,6 @@ path = require 'path'
 async = require 'async'
 pathWatcher = require 'pathwatcher'
 
-configDirPath = fsUtils.absolute("~/.atom")
-
 # Public: Used to access all of Atom's configuration details.
 #
 # A global instance of this class is available to all plugins which can be
@@ -35,27 +33,26 @@ class Config
   configFileHasErrors: null
 
   # Private: Created during initialization, available as `global.config`
-  constructor: ->
-    @configDirPath = configDirPath
-    @bundledKeymapsDirPath = path.join(resourcePath, "keymaps")
-    @nodeModulesDirPath = path.join(resourcePath, "node_modules")
+  constructor: ({@configDirPath, @resourcePath}={}) ->
+    @bundledKeymapsDirPath = path.join(@resourcePath, "keymaps")
+    @nodeModulesDirPath = path.join(@resourcePath, "node_modules")
     @bundledPackageDirPaths = [@nodeModulesDirPath]
     @lessSearchPaths = [
-      path.join(resourcePath, 'static', 'variables')
-      path.join(resourcePath, 'static')
+      path.join(@resourcePath, 'static', 'variables')
+      path.join(@resourcePath, 'static')
     ]
-    @packageDirPaths = [path.join(configDirPath, "packages")]
+    @packageDirPaths = [path.join(@configDirPath, "packages")]
     if atom.getLoadSettings().devMode
-      @packageDirPaths.unshift(path.join(configDirPath, "dev", "packages"))
+      @packageDirPaths.unshift(path.join(@configDirPath, "dev", "packages"))
     @userPackageDirPaths = _.clone(@packageDirPaths)
-    @userStoragePath = path.join(configDirPath, "storage")
+    @userStoragePath = path.join(@configDirPath, "storage")
 
     @defaultSettings =
       core: _.clone(require('./root-view').configDefaults)
       editor: _.clone(require('./editor').configDefaults)
     @settings = {}
-    @configFilePath = fsUtils.resolve(configDirPath, 'config', ['json', 'cson'])
-    @configFilePath ?= path.join(configDirPath, 'config.cson')
+    @configFilePath = fsUtils.resolve(@configDirPath, 'config', ['json', 'cson'])
+    @configFilePath ?= path.join(@configDirPath, 'config.cson')
 
   # Private:
   initializeConfigDirectory: (done) ->
@@ -67,7 +64,7 @@ class Config
       fsUtils.copy(sourcePath, destinationPath, callback)
     queue.drain = done
 
-    templateConfigDirPath = fsUtils.resolve(window.resourcePath, 'dot-atom')
+    templateConfigDirPath = fsUtils.resolve(@resourcePath, 'dot-atom')
     onConfigDirFile = (sourcePath) =>
       relativePath = sourcePath.substring(templateConfigDirPath.length + 1)
       destinationPath = path.join(@configDirPath, relativePath)
diff --git a/src/package-manager.coffee b/src/package-manager.coffee
index cc08c6f56..a2f026b2d 100644
--- a/src/package-manager.coffee
+++ b/src/package-manager.coffee
@@ -8,7 +8,11 @@ module.exports =
 class PackageManager
   _.extend @prototype, EventEmitter
 
-  constructor: ->
+  constructor: ({configDirPath, devMode, @resourcePath}) ->
+    @packageDirPaths = [path.join(configDirPath, "packages")]
+    if devMode
+      @packageDirPaths.unshift(path.join(configDirPath, "dev", "packages"))
+
     @loadedPackages = {}
     @activePackages = {}
     @packageStates = {}
@@ -83,10 +87,10 @@ class PackageManager
   resolvePackagePath: (name) ->
     return name if fsUtils.isDirectorySync(name)
 
-    packagePath = fsUtils.resolve(config.packageDirPaths..., name)
+    packagePath = fsUtils.resolve(@packageDirPaths..., name)
     return packagePath if fsUtils.isDirectorySync(packagePath)
 
-    packagePath = path.join(window.resourcePath, 'node_modules', name)
+    packagePath = path.join(@resourcePath, 'node_modules', name)
     return packagePath if @isInternalPackage(packagePath)
 
   isInternalPackage: (packagePath) ->
@@ -108,11 +112,11 @@ class PackageManager
   getAvailablePackagePaths: ->
     packagePaths = []
 
-    for packageDirPath in config.packageDirPaths
+    for packageDirPath in @packageDirPaths
       for packagePath in fsUtils.listSync(packageDirPath)
         packagePaths.push(packagePath) if fsUtils.isDirectorySync(packagePath)
 
-    for packagePath in fsUtils.listSync(path.join(window.resourcePath, 'node_modules'))
+    for packagePath in fsUtils.listSync(path.join(@resourcePath, 'node_modules'))
       packagePaths.push(packagePath) if @isInternalPackage(packagePath)
 
     _.uniq(packagePaths)
@@ -122,8 +126,8 @@ class PackageManager
 
   getAvailablePackageMetadata: ->
     packages = []
-    for packagePath in atom.getAvailablePackagePaths()
+    for packagePath in @getAvailablePackagePaths()
       name = path.basename(packagePath)
-      metadata = atom.getLoadedPackage(name)?.metadata ? Package.loadMetadata(packagePath, true)
+      metadata = @getLoadedPackage(name)?.metadata ? Package.loadMetadata(packagePath, true)
       packages.push(metadata)
     packages