ArcadeFSE
I built an arcade with three games. My favorite was chess: a chess engine in Python. Expectations were low, but it ended up searching hundreds of thousands of positions per second and playing surprisingly well. Well enough to beat me, at least, though my friends who actually knew chess made quick work of it. I implemented all the rules and game logic from scratch. Learned a ton about minimax, alpha-beta pruning, iterative deepening, and heuristic design.
I used the same core logic for Connect 4. Since Connect 4 is a much easier game, the bot destroyed pretty much everybody. It hadn't fully solved it; if you played against an actual perfect Connect 4 solver, my bot would still lose. But it was pretty good.
And Pac-Man. I didn't really have any care for Pac-Man, but one of my friends had done Pac-Man, and I just wanted to one-up him. So I made that in a couple days and just added it to the thing.