From their technical lead on Quora: http://www.quora.com/Flow-web-application/What-JavaScript-framework-does-Flow-use-for-its-web-frontend/answer/Jason-Webster-

From their technical lead on Quora: http://www.quora.com/Flow-web-application/What-JavaScript-framework-does-Flow-use-for-its-web-frontend/answer/Jason-Webster-2 http://www.quora.com/Flow-web-application/What-JavaScript-fr... jQuery, (customized) Backbone.js, socket.io, and a fair amount of other custom JS.