Things that don't yet fit on any of the lists but are too cool not be mentioned.
A modded game originally known as Super Mario 64. The modder didn't think of a patch system, so the Nintendo ninjas couldn't ignore that unfortunately. There's a copy on Archive.org hanging around though.
A mod for Super Smash Bros. on N64 with a ton more Smashers and stages. Requires a copy of the original game.
Did you perchance mod your DSi/2DS/3DS? With this you can play NDS/DSiWare games without the need of a flash cartridge.