Fixed #1140. I just put it on the home page for now, but later we can put it somewhere where it makes sense.

app/styles/home.sass

@@ -97,6 +97,12 @@
         .code-wizard
           opacity: 0.5
 
+    .language-play-count
+      text-transform: lowercase
+      position: absolute
+      left: 0
+      top: 0
+
     .code-language
       cursor: pointer
       text-align: center
@@ -145,6 +151,8 @@
         background: transparent url(/images/pages/home/language_js.png) no-repeat
         padding-right: 150px
 
+        .language-play-count
+          right: -100px
         .code-wizard
           left: 120px
 
@@ -152,6 +160,8 @@
         background: transparent url(/images/pages/home/language_python.png) no-repeat
         padding-left: 150px
 
+        .language-play-count
+          left: 125px
         .code-wizard
           right: 120px
 
@@ -177,6 +187,10 @@
       .col-md-3
         padding: 0px
 
+      .language-play-count
+        left: 15px
+        top: -15px
+
       .code-language
         background: transparent url(/images/pages/home/language_background_small.png) no-repeat
         width: 250px

app/templates/editor/level/edit.jade

@@ -46,7 +46,7 @@ block header
             span.glyphicon-arrow-left.glyphicon
         li#redo-button(title="Redo (Ctrl+Shift+Z)")
             a
-              span.glyphicon-repeat.glyphicon
+              span.glyphicon-arrow-right.glyphicon
         if authorized
           li#commit-level-start-button
             a

app/templates/home.jade

@@ -11,6 +11,11 @@ block content
           .code-wizard
           h2 JavaScript
           p(data-i18n="home.javascript_blurb") The language of the web. Great for writing websites, web apps, HTML5 games, and servers.
+          - var playCount = codeLanguageCountMap.javascript
+          if playCount
+            div.language-play-count
+              span.spr= playCount
+              span(data-i18n="resources.sessions") sessions
 
       .col-md-6
         .code-language.beta#python(data-code-language='python')
@@ -18,6 +23,11 @@ block content
           .code-language-beta
           h2 Python
           p(data-i18n="home.python_blurb") Simple yet powerful, Python is a great general purpose programming language.
+          - var playCount = codeLanguageCountMap.python
+          if playCount
+            div.language-play-count
+              span.spr= playCount
+              span(data-i18n="resources.sessions") sessions
 
     .secondary-code-languages.row
       .col-md-3
@@ -27,6 +37,11 @@ block content
           .code-language-beta
           h3 CoffeeScript
           p(data-i18n="home.coffeescript_blurb") Nicer JavaScript syntax.
+          - var playCount = codeLanguageCountMap.coffeescript
+          if playCount
+            div.language-play-count
+              span.spr= playCount
+              span(data-i18n="resources.sessions") sessions
 
       .col-md-3
         .code-language.beta#clojure(data-code-language='clojure')
@@ -35,6 +50,11 @@ block content
           .code-language-beta
           h3 Clojure
           p(data-i18n="home.clojure_blurb") A modern Lisp.
+          - var playCount = codeLanguageCountMap.clojure
+          if playCount
+            div.language-play-count
+              span.spr= playCount
+              span(data-i18n="resources.sessions") sessions
 
       .col-md-3
         .code-language.beta#lua(data-code-language='lua')
@@ -43,6 +63,11 @@ block content
           .code-language-beta
           h3 Lua
           p(data-i18n="home.lua_blurb") Game scripting language.
+          - var playCount = codeLanguageCountMap.lua
+          if playCount
+            div.language-play-count
+              span.spr= playCount
+              span(data-i18n="resources.sessions") sessions
 
       .col-md-3
         .code-language.beta#io(data-code-language='io', title="Careful: Io is still quite buggy")
@@ -51,6 +76,11 @@ block content
           .code-language-beta
           h3 Io
           p(data-i18n="home.io_blurb") Simple but obscure.
+          - var playCount = codeLanguageCountMap.io
+          if playCount
+            div.language-play-count
+              span.spr= playCount
+              span(data-i18n="resources.sessions") sessions
 
   .alert.alert-danger.lt-ie10
     strong(data-i18n="home.no_ie") CodeCombat does not run in Internet Explorer 9 or older. Sorry!

app/views/HomeView.coffee

@@ -15,6 +15,7 @@ module.exports = class HomeView extends RootView
   constructor: ->
     super(arguments...)
     ThangType.loadUniversalWizard()
+    @getCodeLanguageCounts()
 
   getRenderData: ->
     c = super()
@@ -28,6 +29,7 @@ module.exports = class HomeView extends RootView
     c.isEnglish = (me.get('preferredLanguage') or 'en').startsWith 'en'
     c.languageName = me.get('preferredLanguage')
     c.codeLanguage = (me.get('aceConfig') ? {}).language or 'javascript'
+    c.codeLanguageCountMap = @codeLanguageCountMap
     c
 
   afterRender: ->
@@ -68,3 +70,19 @@ module.exports = class HomeView extends RootView
     lastButton = @$el.find('#multiplayer .game-mode-wrapper').delay(1000).addClass('hovered', 500).delay(500).removeClass('hovered', 500)
     $('#page-container').animate {scrollTop: firstButton.offset().top - 100, easing: 'easeInOutCubic'}, 500
     @updateLanguageLogos codeLanguage
+
+  getCodeLanguageCounts: ->
+    @codeLanguageCountMap = {}
+    success = (codeLanguageCounts) =>
+      return if @destroyed
+      for codeLanguage in codeLanguageCounts
+        @codeLanguageCountMap[codeLanguage._id] = codeLanguage.sessions
+      @codeLanguageCountMap.javascript += @codeLanguageCountMap[null]
+      @render() if @supermodel.finished()
+
+    codeLanguageCountsRequest = @supermodel.addRequestResource 'play_counts', {
+      url: '/db/level.session/-/code_language_counts'
+      method: 'POST'
+      success: success
+    }, 0
+    codeLanguageCountsRequest.load()

server/levels/level_handler.coffee

@@ -292,8 +292,8 @@ LevelHandler = class LevelHandler extends Handler
     if playCounts = @playCountCache[cacheKey]
       return @sendSuccess res, playCounts
     query = Session.aggregate [
-      {$match: {levelID: {$in: levelIDs}}},
-      {$group: {_id: "$levelID", playtime: {$sum: "$playtime"}, sessions: {$sum: 1}}},
+      {$match: {levelID: {$in: levelIDs}}}
+      {$group: {_id: "$levelID", playtime: {$sum: "$playtime"}, sessions: {$sum: 1}}}
       {$sort: {sessions: -1}}
     ]
     query.exec (err, data) =>

server/levels/sessions/level_session_handler.coffee

@@ -9,6 +9,7 @@ class LevelSessionHandler extends Handler
 
   getByRelationship: (req, res, args...) ->
     return @getActiveSessions req, res if args.length is 2 and args[1] is 'active'
+    return @getCodeLanguageCounts req, res if args[1] is 'code_language_counts'
     super(arguments...)
 
   formatEntity: (req, document) ->
@@ -33,4 +34,22 @@ class LevelSessionHandler extends Handler
     return true if ('employer' in req.user.get('permissions')) and (method ? req.method).toLowerCase() is 'get'
     super(arguments...)
 
+  getCodeLanguageCounts: (req, res) ->
+    if @codeLanguageCache and (new Date()) - @codeLanguageCountCachedSince > 86400 * 1000  # Dumb cache expiration
+      @codeLanguageCountCache = null
+      @codeLanguageCountCacheSince = null
+    if @codeLanguageCountCache
+      return @sendSuccess res, @codeLanguageCountCache
+    query = LevelSession.aggregate [
+      #{$match: {codeLanguage: {$exists: true}}}  # actually slows it down
+      {$group: {_id: "$codeLanguage", sessions: {$sum: 1}}}
+      {$sort: {sessions: -1}}
+    ]
+    query.exec (err, data) =>
+      if err? then return @sendDatabaseError res, err
+      @codeLanguageCountCache = data
+      @codeLanguageCountCachedSince = new Date()
+      @sendSuccess res, data
+
+
 module.exports = new LevelSessionHandler()