Nine little tic-tac-toe boards, one big board, and every mark you make sends your opponent to the board you just played in.
Each of the nine cells inside a small board points to one of the nine small boards. Wherever you play, your opponent must play their next mark in the matching board. Win a small board with three in a row to claim it, then line up three claimed boards to take the game.
Ultimate tic-tac-toe has no recorded inventor and a dozen names — super, meta and strategic tic-tac-toe, mega tic tac toe, (tic-tac-toe)², ultimate noughts and crosses. That spread of names without a source is the signature of a game that circulated by being taught rather than published.
The construction is a single idea applied to itself: nine tic-tac-toe boards arranged in a 3×3 grid, where winning a small board claims that cell of the large one. What turns it from a novelty into a game is the constraint that your move dictates which board your opponent must play in next.
That one rule breaks the parent game's fatal flaw. Ordinary tic-tac-toe is a solved draw that any adult plays perfectly; this version is conceptually harder for people and has proved notably harder for computers, because a move must be judged on both boards at once.
This is a layered take on the classic noughts-and-crosses grid, turning a quick draw-prone game into a deep nesting puzzle of forced moves. It is an original, free browser game with no download or sign-up required.