Robocars find racetrack in every room
Here's how fritsl, the maker, describes the hardware and control:
Wall Racers was made by 2 cheap (and crap driving) RC cars. I gave them sensors (SRF05), tuned with an extra battery, and gave them own logic / "robot-brains" (Picaxe 28).
Primary target is to stay close to the wall, drive fast, and overtake the other :)
He says he wants to market this as a toy (he's looking for partners), which sounds like a great idea. In the meantime, you can find instructions here to make your own.