Glitch - Glitch is the friendly community where everyone builds the web. Simple, powerful interface for creating web apps.
CodeKeep - Codekeep lets you store and share bits of code and text with other users. Snippets can be organized into folders/labels for instant reuse.
Koji - Develop and deploy web apps at a ludicrous speed
Anyfiddle - Build, run and share code in any language from your browser
StdLib - Discover pre-built APIs, compose your own and build apps
CodeMyUI - Handpicked code snippets you can use in your web projects