Pokegb: A gameboy emulator that only plays Pokémon Blue, in 68 lines of C++
I did something similar with an X86, with enough opcodes implemented so it could run Goody (an ancient CGA game): <a href="https://gabrielgambetta.com/remakes.html" rel="nofollow">https://gabrielgambetta.com/remakes.html</a> Super fun exercise!