Mupen64 is a n64 emulator desgined to be multi-OS. It has been developped on/for Linux originally but the emulator has already been ported succesfully on Windows and MacOSX for example. Actually the program can be easily ported on all OS supported by the SDL library.
In its current state, the emulator is highly compatible and use a plugin system. With the correct plugins (“correct” can be computer dependent), it can achieve nearly perfect graphics and sound in many games.
The biggest problem of this emulator until now was its speed but now it’s progressively changing with a totally new core and there’s still a huge room for improvements. Anyway if you have a fast machine, you should already be able to get many games running fullspeed.