Vassal is a game engine for building and playing online adaptations of board games and card games. You can use Vassal to play in real time over the Internet or by email. Vassal runs on all platforms and is free, open-source software.
Thousands of boardgames have been converted into Vassal modules. If there is not yet a Vassal module for your favorite game, you can use the Vassal Editor to build your own module.