Created by Chris Coyier (CSS-Tricks, Shoptalkshow), Tim Sabat and Alex Vazquez
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 examples of a particular design pattern for your project? CodePen is great for that.
CodePen PRO takes things further with features like Collab Mode which allows you to pair program in real time and Professor Mode for allowing a group of students to follow you as you teach code and chat with each other.
It is essentially pastebin/jsbin crossed with GitHub and more.
You can create public ‘pens’ that people can fork
You can create private pens
People can love/favourite pens, comment on pens and more.
Free and Paid Plans
There is a free tier, yay, there are also paid tiers, starting from $9 to get the pro features such as, unlimited private pens, live view, asset hosting, collar mode, professor mode, custom css on your profile, blog, embed themes with custom css (as many as you like), send to phone messages and more as the plans go up.
There is the Codepen blog filled with awesome juicy info.
Then there is Codepen radio, you must subscribe, there is so much great content for development in general, running a startup/saas product and more.