React
JSFiddle just announced support for React. This is an exciting news as it makes collaboration on snippets of code a lot easier. You can play around this base React JSFiddle, fork it and share it! A fiddle without JSX is also available.
React (by Facebook) is now available on JSFiddle. facebook.github.io/react/
— JSFiddle (@jsfiddle) June 2, 2013