A MOVE IS TWO THINGS
First you drop a stone into the face that is currently up: pick a column with the arrows or the mouse, SPACE or click to let it go. Then you turn the cube a quarter turn with I, K, J or L — and whichever face ends up on top is the face your opponent has to play into.
FOUR IN A LINE
Four of your colour in a straight run wins it, anywhere in the cube: along an edge, flat across a face, or corner to corner through the middle. Sixty-four cells, seventy-six lines.
STONES DO NOT MOVE
A stone travels until something is in front of it and then it locks into the lattice. Turning the cube does not shake anything loose — what it changes is which direction the next stone falls from, and therefore which cells anybody can still reach.
THAT IS THE WHOLE GAME
You can see the cell that would finish their line. You cannot take it away, but you can turn the cube so it is buried — so it is no longer the first cell a stone meets coming in. Give yourself two ways to finish and they can only bury one.