Tic Tac Toe
Pick 1 Player to face the computer or 2 Player to share the board. You are X and always move first. The running tally is per visit.
Developer Note: this is a 2011 Java applet rebuilt for the browser. The opponent is the original's minimax search, carried over intact — it solves the whole game tree, so it cannot be beaten and a draw is the best result available. The applet drove that search from a background thread that busy-waited on mouse coordinates; browsers have no such thread, so the game loop was rewritten as an event-driven state machine around the same algorithm. The original also wrote every result to a MySQL database over the open internet — that is gone, and the score is kept in memory.