Hosted by Harbour Masters who also provide ports for other Nintendo classics, the PC port of Mario Kart 64 is now available to test. Completely unofficial of course just like the ports of Star Fox 64, The Legend of Zelda: Ocarina of Time and Zelda: Majora's Mask.
Named SpaghettiKart, it does not include any copyrighted assets. You are required to provide a supported copy of the game that you own, so hopefully this will continue to keep it away from Nintendo lawyers. It adds in support for Windows and Linux, a Harbour Masters themed track, higher resolutions and rendering distance, an editor to import tracks from Blender and more. It's still a work in progress, so some issues are to be expected.

Direct Link
It will be interesting to see what the modding community comes up for it, and for what game they're going to be porting to PC next.
You can find it on their GitHub. It has an AppImage download for Linux. There doesn't seem to be an actual license attached to the code just yet.