Three-dimensional tic-tac-toe with a twist: chase four in a row through a 4x4x4 cube, where lines hide in diagonals you can barely see, and you can rotate a layer once to wreck them.
The cube is shown as four stacked 4x4 layers side by side. Players alternate placing their mark in an empty cell. The goal is four of your marks in a straight line anywhere in the cube, there are 76 possible winning lines.
This is 3-D tic-tac-toe, sold commercially as Qubic: a 4×4×4 array, four in a row to win, and lines that run along a single layer, up a column, or diagonally through all four boards. There are 76 of them.
Showing the cube as four stacked layers side by side is a presentation choice, not a rule change — the geometry is the original's.
Qubic is a solved game with a published first-player win, and the reason it still plays well is in the article's own observation: the strategy is too complicated for most people to memorise. Seventy-six lines through a space you are viewing as four flat squares is simply more than human pattern-matching handles.
Cube Four reimagines three-dimensional noughts-and-crosses as an original, free browser game, adding a once-per-game layer rotation, three CPU strengths, hotseat and online play.