Stringdrive

http://www.stringdrive.com

The STRINGDRIVE® has two identical but oppositely directed driving units, and as we turn the pedals, the task of driving is unnoticeably transferred from the right to the left sides and vice versa. It is the result of state of the art design technique that even the most sensitive driver cannot feel when the driving is shifted from one side to the other. Once you have experienced this symmetry, you will feel the ease of driving, the ease of maneuvering and of keeping balances in all positions combined with the smooth feeling provided by the rope used instead of the chain.

http://www.youtube.com/watch?v=z4PAzalfpww