Dolphin is a GameCube, Wii and Triforce (the arcade machine based on the GameCube) emulator which supports many extra features and abilities not present on the original consoles. GameCube and Wii compatibility is good - one can expect "mainstream" titles to run; lesser known titles can be hit or miss. Triforce compatibility is currently limited to a couple of games - others require more of the Triforce-specific peripheral devices to be emulated.
