Ultimate tic-tac-toe

Ultimate tic-tac-toe is a board game built from nine ordinary tic-tac-toe boards laid out in a three by three grid, so that the small boards together form one large board. Two names for it in circulation are super tic-tac-toe and meta tic-tac-toe, and it is also sold or described as Ultimate Noughts and Crosses. Players take turns marking squares on the smaller boards, and the contest ends when one player wins on the larger board. The extra layer makes its strategy conceptually harder than the familiar game it extends, and it has proven more challenging for computers to play well.