[icefo]

If you don't mind french, the project of this class that introduces OO programming was really great: https://cs108.epfl.ch/archive/18/archive.html

It guides you through making a Gameboy emulator step by step. When I did it I remember that something that was a bit frustrating is that you had to do things a certain way that only made sense much later when other pieces of the puzzle fell into place