A friend saw this cruising around the Arizona State campus: Chris Coleman, a sculptor, has made a self-balancing one-wheeled skateboard based on Ben Smither’s design. He fabbed the metal frame himself, used an Arduino microcontroller, and published his code. Incredible; great job!
Self-balancing one-wheeled skateboard – Link.
Homemade balancing one-wheeled scooter on MAKE – Link.