Noughts and crosses
Noughts and crosses, also known as tic-tac-toe is a game.
It uses a 3x3 grid, and two players (or teams), one playing nought (O) and the other crosses (X), with the aim being to complete a three-in-a-row of one's. With perfect play, it is a draw, but can be easily modified; "answer a question correctly" for the chance to play, but if you answer incorrectly your skip a turn. Great fun.