The Game of Amazons
For information about the rules of the game, check out the wikipedia page.
To play the game, I have it hosted on my website here.
This is an implementation of the game, done completely using the HTML5 canvas tag. So, to play the game, you'll need a modern browser.
For now, there is no AI player. And there may never be one.
Also, you can just pretty much play against yourself, or with another person sitting beside you at the same computer.