@coolboymew There's a huge ton of unrelease GB/GBC stuff. There's even source code for the Work Boy which was some OS for the GameBoy that turned it into a PDA of some sorts. It even had a keyboard.
@1iceloops123 @coolboymew I heard that people are compiling the ROMs with varying degrees of success. I can imagine Nintendo writing their own compilers/assemblers during the NES, SNES, and GB eras. I remember seeing footage from Nintendo's offices back in the 80s. Apparently, they had IDEs running on Famicoms.