sixtyforce is an emulator that runs Nintendo 64 games. It does this by dynamically translating the code that a Nintendo 64 uses into something your Mac understands. Nearly every part of a Nintendo 64 has been painstakingly recreated entirely out of software to pull off such an amazing feat.

More screenshot here: http://www.sixtyforce.com/screenshots/

Requires Mac OS X 10.2 or later and at least a G4 or Intel Mac with 3D graphics acceleration.