The Tensegrity Foot, doubtless named for Buckminster Fuller's concept which uses pushing and pulling forces to maintain a balance, takes a very different approach to pedal prosthesis. Instead of using countless fragile and finicky computer controlled servo motors, Jerome Rifkin's device is mostly passive:

Prosthetics don't really do what feet do. The human foot doesn't actively do that much when you;'re walking. It's a fairly passive device. You just have to set it up correctly and let it do what it naturally does.

Rifkin's foot is essentially a few machined magnesium blocks connected by steel cables and springs. The flexing of these sections doesn't mimic the actual human foot (the ankle doesn't bend, for example) but it transfers force and springs back in a similar way. The (non embeddable) video shows the feet in action. Aside from the squeaking, and the big ski boots needed for an able bodied person to test them, they look pretty natural.

The Natural Artificial Foot [Popsci via BBGadgets]