Link Four

Drop a stone into a column, it falls to the lowest free slot, and the first player to line four of them up — across, down or diagonally — takes the round. Link Four is that game, the one usually played with a plastic frame and a sliding tray, against a computer that gets genuinely harder across five difficulty settings. The top level is good enough to punish the trap everybody uses first: build a position where two different columns both finish a four, and the block cannot cover both.