Several years ago I built a simple snake game and wrote a DQN from scratch to learn how to play it.

I was really proud of it at the time because I had to do a decent amount of reading and research since I wrote all of the NN code from scratch and wanted to add some more advanced algorithm optimisations which I hadn't done in previous projects.

I suspect a coding agent could spit the entire project out in 20 minutes now, but it was very cool at the time to build a game then watch my computer learn how to play it in real time.