Well, all this reading about the board game Hex made me want to play. Six is an interesting, capable hex player available for Linux. It's really very slick, it plays on any board size from 4x4 to 14x14, and at multiple difficulty levels. I've only played a few games, but have already learned a lot. Here's the board from one of my 10x10 games where I played white. I lost, but I thought I did okay in defending.
I'm already learning a lot. One of the neater things about Hex is that since pieces don't move after you play them, the entire game is right there.