3D Tic-Tac-Toe is a version of tic-tac-toe that has been extended into three dimensions, but is otherwise identical to it's two dimensional counterpart. The easiest way to visualise this is a cube divided up into 27 smaller cubes, which are arranged in a 3x3x3 array. Players take it in turns to place an X or an O into a cube, and the first one to place three in a row wins.