This is one of those projects that’s just all around cool: Anders Granlund is bringing Wolfenstein 3D to the GameBoy Color, and since the GBC is quite hardware-constrained, he needs to employ some extreme measures to accomplish this. One of these measures is to add a co-processor into the game cartridge.
Somebody apparently ported Doom to the Commodore Vic-20:
https://www.youtube.com/watch?v=WFMM3F_-bx0&t=1s
And of course, there’s always Grand Theft Auto IV for Intellivision. Because Atari sucks balls
https://www.youtube.com/watch?v=ZdHG5-K8E1E
Edited 2016-12-20 05:20 UTC
The addition of the co-processor is a nice touch. Tons of those were used in various cartridges, though, I’m not sure how many found their way into Game Boys.
Still, though. I dont’ consider it cheating, as it is only optimizing use of the GBC’s way of doing color.
There were definitely some used for audio, but I don’t think I’ve heard of one being used for anything else.
As long as the extra processor fits inside the cartridge, I think it’s fine. *Remembers the Magnavox Odyssey^A^2 Chess cartridge…*