What are some alternatives?
Koding - A new way for developers to work.
CodePen - A front end web development playground.
Codeanywhere - Codeanywhere is a complete toolset for web development. Enabling you to edit, collaborate and run your projects from any device.
JS Bin - Sample of the bin:
AWS Cloud9 - AWS Cloud9 is a cloud-based integrated development environment (IDE) that lets you write, run, and debug your code with just a browser.