Shift Trike Bike
The SHIFT looks like a tricycle but changes to a bicycle when you speed up and back to a tricycle when the you slow down:
The design features a single front wheel and two slim rear wheels that are initially splayed outward to stabilize and prevent the rider from toppling over. As the rider accelerates and leans forward, the rear wheels shift inward, narrowing into a single wheel surface that essentially makes it a two-wheel venture.
It looks cool and it helps kids face the most difficult, and scary, parts of learning to bike; starting and stopping.