Per above, go to BentRiderOnline.
One interesting possibility are delta trikes (1 wheel in front, 2 in rear) which can be linked into an articulated tandem or used as two separate trikes. I know Hase makes tricycles with this capability (they once linked up dozens of them for a world record 150 meter (about 490 feet) long cycle (bicyle=2 wheels, tricycle=3 wheels, about 3*90 wheels= centicycle?). I also believe the Greenspeed Anuras can be coupled together in a similar manner.