Tic Tac Toe
This implementation features perfect AI; it will always choose a move that will lead to a win, if possible. Perfect AI comes at a cost, however: it recomputes the game tree on every move, an expensive process that has a recursion within an iteration. I've hard coded in the AI's first move, but you'll notice a substantial thinking time on its second move, roughly 10 seconds.
As it's an html page, you can visit the Github Pages version of this repo to see it in action.