CodePen is a social development environment for front-end designers and developers. It’s the best place to build and deploy a website, show off your work, build test cases, and find inspiration.
CodePen - Details & Top Features
CodePen hosts an amazing collection of frontend code snippets called 'Pens', thanks to its huge user base. CodePen offers a great UI, an online editor and preview making it a must-have for any serious frontend developer.