CodePen - A front end web development playground.
Koding - A new way for developers to work.
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
goormIDE - goormIDE is a cloud IDE service to maximize the productivity for developers and teams. Develop and deploy your service with powerful collaborative features, anytime and anywhere.
JS Bin - Sample of the bin:
Codiad - Codiad is an open source, web-based, cloud IDE and code editor with minimal footprint and requirements