Two castles, separated by a mountain, try to defeat each other with their cannonballs, either by killing the opponent's king or by weakening the opponent enough so that the king capitulates.

Ballerburg was originally written 1987 by Eckhard Kruse, for the Atari ST machines (which were brand new computers at that point in time). Over 25 years later, here's finally the adaption of the original source code to modern operating systems.