What is Vassal? (From Vassalengine.org)
Vassal is a game engine for building and playing online adaptations of board games and card games. Play live on the Internet or by email. Vassal runs on all platforms, and is free, open-source software.
Where to Download?
The Vassal module includes all maps and counters required to play the game.
VASSAL Setup - Attack on Railway Station
VASSAL Setup - Balloon Busting