Play 4-Dimensional Tic-Tac-Toe here. 4-Dimensional Tic-Tac-Toe takes longer to play than ordinary tic-tac-toe and is much more challenging. Tic-tac-toe is also known as noughts and crosses (can also be spelled naughts and crosses or Os and Xs). The game on this site is called tic-tac-toe because it is based on a grid of 3x3 squares. Some games use a 4x4 matrix instead. To play noughts and crosses in three dimensions, make three tic-tac-toe grids and call them Upper Middle and Lower. There will be 27 squares, but the middle square will provide so much benefit to the player who takes it that it makes the game trivial again. So in 3-D O's and X's and 4D Tic-Tac-Toe the middle square is unavailable to either player. In Four dimensional O's and X's there are 81 squares cut down to 80 as the middle square is unavailable. Playing 4-D tic-tac-toe can help to exercise your pattern recognition and short term memory skills. The activity of thinking ahead and pattern recognition tasks can help train your brain and helps to counteract the ageing process.