Object:
Black and White alternate dropping pawn or king disks. Pawns are placed on vacant squares; kings are placed over pawns. Each disk must be placed so that it sandwiches one or more enemy pieces between itself and another friendly piece, with no empty squares intervening. The sandwiched enemy pieces are flipped, changing colour.

If one player can't move, he must pass his turn.
The game ends when neither side can move, usually when the whole board is filled. The winner is the player with the most on-board pieces (both king and pawn disks) of his colour.

based on Zillion's Reversi v1.2
SPECIAL NOTE: the Jello.dll engine has been left out.