Tic-Tac-Toe

Everyone knows tic-tac-toe, and everyone eventually discovers its dark secret: played perfectly, it always ends in a draw. That makes this version against the computer a nice little test of whether you actually play it perfectly. You are X, the machine is O, and you are hunting three in a row across, down, or diagonally — but the interesting layer is the two difficulties. Easy leaves openings you can pounce on; Hard uses flawless strategy and simply cannot be beaten, so the most you can wring out of it is a stalemate. The winning ideas are small but real: seize the centre when it is free because it feeds the most lines, grab a corner rather than an edge if you move second, and — the move that actually wins games — build a fork, two threats at once, so a single block can never cover both. And always, always block the machine the instant it shows two in a row. Free, instant, no sign-up, with your running tally of wins, losses, and draws kept between games.