Shareware versions are available. Pieces are disks with one side black, the other white. Players take turns putting disks on the board. When your play brackets the other guys pieces, they flip over to your color. The dominant color of the board can change alarmingly fast as play moves from the center to the edges.
Corners are mondo cool.
Simple to learn. Absorbing to play. 2 players ages 9 and up. About 15 minutes per game. This is one of our favorite two-player strategy games.