Connect Four offers a plastic version of the classic tic-tac-toe, played with plastic checkers. This Milton Bradley product first appeared on the game scene in 1974 and has remained popular ever since. Players slip black or red checkers into slots on a vertical board. The object of the game is to have four checkers of the same color in a horizontal, vertical, or diagonal row before your opponent. Because the board itself sits in a vertical plane, gravity becomes a factor. Each player needs to consider gravity in placing his or her four checkers in a row without contributing to the opponent's success. The game's concept wasn't particularly innovative; tic-tac-toe has been around since before pencils, and the checkers used in the game had long been a staple of every nursery and playroom. And this particular version was played on ships, on wooden racks, long before 1974.