CodePen - A front end web development playground.
GitHub Gist - Gist is a simple way to share snippets and pastes with others.
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
Ghostbin - Ghostbin is an open source paste service.
replit - Code, create, andlearn together. Use our free, collaborative, in-browser IDE to code in 50+ languages — without spending a second on setup.
JS Bin - Sample of the bin: