Site Name : CodePen.io
url : http://codepen.io
CodePen is a playground for the front end side of the web. It’s all about inspiration, education, and sharing.
Need to build a reduced test case to demonstrate and figure out a bug? CodePen is great for that. Want to show off your latest creation and get feedback from your peers? CodePen is great for that. Want to find example of a particular design pattern for you project? CodePen is great for that.
You can run your HTML , CSS , Js and other code online.
Really it is good tool for devloper.