The BrickPi is a Raspberry Pi shield that can control Lego Mindstorms robots, replacing Lego’s proprietary microcontroller brick.
One interesting angle Dexter took was actually making the shield Arduino based. The shield consists of two surface-mount ATMega328 chips that control two motor control ICs and take input from 5 sensors, in part using code from Wayne & Layne’s open source Lego-controlling Arduino shields.
What is intriguing about this angle is that it could be used for any microcontroller. It could just as easily be a BeagleBone or PCDuino under the shield, because the Pi is mostly just sending pings while the ATMegas do all the hard work.