Vassal_Engine
The Vassal Engine is a game engine for building and playing online adaptations of board games, tabletop games and card games. It allows users to play in real time over a live Internet connection, and also by email (PbeM). It runs on all platforms, and is free, open-source software.[1][2] For example, there is a Star Wars Miniatures module, where players can play with up to three others in a digital replica of the table-top game.
It is written in Java and the source code is available from GitHub under the LGPL open source license.[3]