The Handy Board is a small computer that is ideal for LEGO robotics projects. These pages contain some basic information about the Handy Board along with tips on how to use it with LEGO.
The Handy Board is a small computer based on the Motorola 68HC11 microprocessor. This board includes control for up to 4 motors, 9 digital inputs, 7 analog inputs, Infrared communications, and a 16x2 character LCD display. Complete schematics and PC layouts are available at the MIT site. Several vendors of built and tested boards are also listed. Other options include purchasing a kit, or buying the PC board and building it yourself.
Although the traditional embedded programming tools can be used with the board, Interactive C appears to be the development language of choice. There are two basic versions: the free one and the commercial one. The free version has two advantages: it is free, and complete source code is available (for those of you who may want to modify it). The commercial version is relatively inexpensive ($35 for personal/educational use), and provides a slightly more features along with a very nice Integrated Development Environment (IDE). If you don't plan on doing any custom modifications to the development tools or runtime, I'd suggest buying the commercial version.