I made this applet in grade 7 to learn Java. It allows you to play the game Ultimate Tic-Tac-Toe against an AI.
For an interesting overview of the game visit Math With Bad Drawings.
The AI is based on the minimax algorithm with many heuristics. The problem is this game has so much strategy that I could not balance the parameters right so the AI is not very good.
To see some of my work that is not four years old visit my website.