There are a couple of options that I'm aware of. The first is Vassal, which is a free to use set up that creates a virtual 2-D tabletop where you can move models, roll dice, etc. There are various "modules" that you can load for various games; a few of us here on the MBS forums have been using it to run a Battlefleet Gothic campaign the last few months. These modules are all fan-made and supported (sort of like the data files for LoneWolf's Army Builder). However, they don't have modules for all the games out there, and some of the modules (like the BFG or FSA ones) haven't been updated in a while. There are some bugs, and the controls are a bit clunky, but hey, it's free!
The other option is a game called Tabletop Simulator, which you can find on Steam. This game has full 3-D graphics, but otherwise works on a similar model as Vassal. I know that there is a Halo Fleet Battles module for it, not sure about the rest of the Spartan Games. Another downside is that you have to buy the base game.
