Super Mario 64 re-imagined as a multiplayer game, created after dozens (if not hundreds) of grueling hours of reverse-engineering. jailbroken Wii (so you can load a homebrew WAD file) or an N64 PC emulator. Super Mario 64: Split-screen Multiplayer -The lack of multiplayer action in Super Mario 64 bothered one game modder so.
Wii VC mode handles VC WAD titles while Nintendo 64 mode. Downloads: SMSR Multiplayer 1.2.1 (Mirror) SM64 Multiplayer 1.4.2 SM64 Multiplayer 1.3.1 MEGA Decryption Keys. I've also included the extensive documentation for those interested.