3-D Tic-Tac-Toe

3-D Tic-Tac-Toe is a video game released by Atari, Inc for the Atari 2600 console and Atari 8-bit computers in 1980. The game is similar to the traditional game of tic-tac-toe, but is played on four 4×4 grids stacked vertically; it is basically a computerized version of the board game Qubic using traditional tic-tac-toe notation and layout. To win, a player must place four of their symbols on four squares that line up vertically, horizontally, or diagonally, on a single grid, or spaced evenly over all four grids. This creates a total of 76 possible ways to win, in comparison to eight possible ways to win on a standard 3×3 board. The game has nine variations: it can be played by two players against each other, or one player can play against a built-in AI on one of eight different difficulty settings. The game uses the standard joystick controller.

3-D Tic-Tac-Toe for Atari 2600 was written by Carol Shaw, who went on to greater fame as the creator of Activision's River Raid. The game was remade for the Microsoft Entertainment Pack as TicTactics; this version also allowed the game to be played inside a 3×3×3 grid.

On the 4×4×4 board, there are 76 winning lines: 48 that are parallel to an edge of the cube, 24 that are parallel to a face diagonal, and finally 4 body diagonals of the cube. The 16 cells lying on these latter four lines (that is, the eight corner cells and eight internal cells) are each included in seven different winning lines; the other 48 cells (24 face cells and 24 edge cells) are each included in four winning lines.

3D tic-tac-toe was weakly solved, meaning that the existence of a winning strategy was proven but without actually presenting such a strategy, by Eugene Mahalko in 1976. He proved that in two-person play, the first player will win if there are two optimal players.