Not Quite C is a programming language and compiler designed for the Lego smart bricks -- originally just the Mindstorms RCX, but now also Cybermaster and Scout. It's very like the C we all know and love, but due to restrictions in the Lego firmware (most obviously -- it's limited to only register variables) it's not quite a complete language. (Hence the name.) However, it's far far better than the official software.

Runs on Linux, Win32, MacOS, and anything else you care to port it to.