The developers behind Canabalt confirmed that the game's source code will be made available as part of an open source project. The game will be licensed under the MIT Open Source license, which will let other developers use the engine source code in its entirety for both personal and commercial projects. While the code powering the game is available for the world to use, the game art, sounds, animations and Canabalt game-specific code is still proprietary. Basically, you cannot re-package their game and claim it as your own, but you can use the underlying engine code to power your own game.
The developers warn prospective