CodePen - A front end web development playground.
Appcelerator Titanium - Appcelerator Open Source
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
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JS Bin - Sample of the bin:
Onsen UI - HTML5 Hybrid Mobile App UI Framework - work with Angular, React, Vue, Meteor & pure JavaScript. Material & Flat design.