Vassal is "pretty big" in the 40k world, I'm not sure about the Fantasy world. It's a GUI, much like the screen shots are showing on UniBats, but capable of handling a bunch of different things. When I say things, I mean board/table top games.
http://www.vassalengine.org/
http://www.vassalengine.org/wiki/Module:Warhammer_40,000
I'm not seeing the Module for Fantasy on Vassal's page. To be fair, 40ks isn't on there, either, though, because Copyright.