CodePen.io

Developers Chris Coyier, Tim Sabat, and Alex Vazquez founded CodePen to give developers and designers of any skill level the option to edit front-end languages in a browser-based code editor, visualizing results in real-time. Users would create “pens,” snippets of code that could be shared with other users. Frameworks, libraries, and UI patterns were organized into topics where users could browse and request specific resources.