This Google Chrome extension displays JavaScript frameworks used on a website.
It can be found here in the Chrome extension library.
It's inspired by bookmarklets like WTFramework.
ActiveJS*, AngularJS, Backbone.js, Base2, Clientcide Libraries, Crafty*, Cufon*, d3.js, DHTMLX*, Dojo, Ember, Ext JS, Glow, JavaScriptMVC*, jQuery, jQuery UI, Knockout.js, Midori*, Modernizr, MochiKit, MooTools A.R.T., MooTools Core, MooTools More, Processing.js, Prototype, Qooxdoo, Raphaël, RequireJS, Rico, RightJS, Sammy.js, Script.aculo.us, Scripty2, Snack, Spine, SproutCore*, Spry*, Underscore.js, YUI, Zepto*, ZK
*) no version detection
(in order of first commit)