Just a few days ago a huge Super Mario 64 Romhack / Mod was released: https://romhacking.com/hack/mario-builder-64 or alternative link: https://gamebanana.com/mods/514361 As usual, it’s a patch file that needs to be patched on top of original Super Mario 64 Rom for the Nintendo 64: https://www.romhacking.net/patch/
I’ve just tested it and runs great on RetroArch! This mod is impressive. It’s a level editor for Super Mario 64 in Super Mario 64 itself and reportedly runs on original hardware as well. The user interface is very simple, it has lot of stuff to add in the levels.
The only problem is, RetroArch or the core does not support SD cards to save level creations or load from others. They recommend a tool named Parallel Launcher, which runs ParallelN64 core from RetroArch, but I think without RetroArch. Here a few screenshots (made in RetroArch):
