Vassal is a Java-based program that allows you to play World in Flames online with your friends. To use that, you need a minimum of 2 things the Vassal Game Engine and the Gamebox, plus optionally a saved game for starting new games (the latter will save you countless hours of force pool creation and fleet setup).
Vassal game engine is here : http://vassalengine.org/.
The CE game box is currently in developpment by Craig Walters working with ADG (http://dddgamedesigns.com/vassal-products/).
Voici une aide en français.