It's a dual H-bridge using power MOSFETs.
I designed and built my own power MOSFET drive, but was having trouble blowing up MOSFETs and frying gate resistors. I believe the problem lies in some bad MOSFETs I got off of ebay. My drive did work for a little bit.
Anyway, I also bought a Dimension Engineering Sabertooth 2X25 drive. I have it driving wheelchair motors for my yard robot. So far I've only done a bench test, but the performance of the Sabertooth is quite a bit better than my home-made drive. Very good low speed torque, fast stopping, quick throttle response. And a great small package. The only complaint I have is that I emailed their tech support a question and it was never answered.