I ported Forth to a 1980s sampler, so that you could plug a MIDI cable in and run a special terminal program to write Forth programs on its 6809 processor.

It boots off a floppy disk, so it was really just a case of working out where in the ROM and OS disassembly the entry points were, and making it all fit around the assumptions the ROM makes.

This allowed me to make up a diagnostics disk to check the RAM (a whopping 128kB of sample RAM) and IO are working.

https://gordonjcp.github.io/miragetools/

Now I wouldn't place a bet on it being the nerdiest project on Github, but I suspect it's well up there.