CodeCombat is a multiplayer programming game for learning how to code. See the Archmage developer wiki for a dev setup guide, extensive documentation, and much more.
It's both a startup and a community project, completely open source under the MIT and Creative Commons licenses. It's the largest open source CoffeeScript project by lines of code, and since it's a game (with really cool tech), it's really fun to hack on. Join us in teaching the world to code! Your contribution will go on to show millions of players how cool programming can be.
We've made it easy to fork the project, run a simple script that'll install all the dependencies, and get a local copy of CodeCombat running right away on Mac, Linux, or Windows. See the docs for details.
Whether you're novice or pro, the CodeCombat team is ready to help you implement your ideas. Reach out on our forum, our issue tracker, or our developer chat room, or see the docs for more on how to contribute.