I made a very basic Tic Tac Toe game. For this one I tried to build it all within an entire screen - while Hangman jumps around and transitions from screen to screen, this game is just a single screen that gets re-used when the game is over (or replayed).
Over the course of building this, I also wound up with some utility code that makes text formatting and transitioning from screen to screen a little simpler. And I discovered that I don't really enjoy writing AI code.
If I'd spent a little bit more time working on the AI I could have made it actively block you; while I was researching I found some code to do it, but I figured this was good enough for now. I'm bad enough at Tic Tac Toe that it still beats me periodically, apparently.