Bicycle maker Gyrobike has invented the "Gyrowheel" -- a wheel with a motor-driven gyroscope inside that helps keep it upright. The manufacturer hopes to market it as a replacement for traditional training wheels on kids' bicycles. Nathan Barry of GeekDad writes:
It aims to replace traditional training wheels or stabilizers and to eradicate the bad habits that they teach kids when learning to ride a bike - leaning away from a turn and constantly putting a foot down at the first sign of a wobble when they’re eventually taken off. The Gyrowheel uses the “gyroscopic precession” of the independently spinning disk inside it to stabilize the bike. The force created when the disk is turned - via a rechargeable battery - is powerful enough to hold a wheel upright at very low speeds (i.e. virtually stopped), and can actually make a bike look like it has a “Ghost Rider” as the videos below show (and there are plenty more on the Gyrobike site).
Product Page via GeekDad (where there's an additional video)