Take turns dropping a disc into one of the seven columns. It falls to the lowest empty space. A full column takes no more discs.
Line up four of your discs across, down or diagonally to win the round. If the board fills up first, the round is a draw.
Scores carry across rounds, and the starting player alternates each round.
Red discs carry a cross and Blue discs a ring. Keyboard: Left and Right pick a column, Enter or Space drops a disc, Ctrl+Z (Cmd+Z on a Mac) undoes.