As a fun side project, I built this awesome Tic-Tac-Toe game (with three AI levels) in May 2017.
@microwither I think it would be cool if you tie against the computer, The program doesn't end. So that you can keep going without having to start the program again.
Maybe adding an option asking if you want to play again.
@jeremiah32556: Thanks for the suggestion! I think I'll just leave it as it is until more people want this though.
@jeremiah32556: That sounds like a great idea.