The Scott Self Energizing. Excerpts taken from the late Sheldon brown:
Self-Energizing Cantilevers Because of the myth that conventional cantilevers aren't strong enough for tandem use, some people favor Self-Energizing cantilevers. These don't have a simple pivot, instead, each arm moves on a steep multi-start screw thread, so that as the shoe approaches the rim it also moves forward. When it rubs on the moving rim, the forward pull tends to increase the inward pressure, providing a "positive feedback."
This design can apply greater braking force for less finger force than a conventional cantilever, but it is difficult to modulate it. The original Scott Pedersen SE brakes were available either for front or rear use (opposite direction threadings), but when
Sun Tour bought the design, their legal department vetoed the front version, so only the rear model was made by Sun Tour. I advise against the use of Self Energizing brakes, because they make it too easy to lock up the wheel.
whew....me personally, glad to be locking the rear wheel with discs.
