Scratch: MIT Language for Creating Games, Music, Art, and More

The MIT Media Lab's Lifelong Kindergarten Group created the Scratch programming language that makes it easy to create your own interactive stories, animations, games, music, and art -- and share your creations on the web (description from their website). It is available as freeware for Mac OS X and Microsoft Windows. A version for Linux is currently being developed according to the note on the download page. You can learn more about working with Scratch on its Informational Page.