0 and x is a 3D version of Tic-Tac-Toe or Noughts and Crosses, where you have to make a row of X's in a vertical, horizontal or diagonal line before the computer makes a row. Instead of making a row off three on a 3 x 3 grid you now have to make a row off four on a 4 x 4 grid on four boards so as well as watching for a line on one board, you have to watch out for a row that appears in the same place on all four boards.