Swift Office Ships
is a clone of the classic game Battleships. The only thing that differs is that Swift Office Ships is played on a Mac in a Bonjour (formerly Rendezvous) network instead of a piece of paper. If there is no other player available you can also play it against a computer opponent.
The bad news is that cheating isn't possible, so e.g. you cannot place your very last submarine while the game is already in progress ;-)