I'm a really big fan of Robin Fitton's Gruntz rules. I first saw them being demo'ed on his awesome urban terrain board at SELWG 2 or 3 years ago, and I've followed and contributed a bit to their development since then (there are a few pieces of my flavour fiction in the rulebook).
One of the things I especially like is the unit builders. You can essentially build any unit you like, from any background, any tech, any race, any figure line and stat it up. You could have ultra hi-tech GZG hardsuited New Israeli commandos fighting against Khurasan Miniatures Lhurgg tribesmen, or Rebel Minis Sahadeen fighting against CMG Kaamados. There have even been unit stats produced for British colonial troops - pith helmets and short chamber Boxer Henry point 45 calibre rifles, with a bayonet and some guts behind it.
Robin has started a kickstarter campaign on Indegogo to launch a computerised version of the army builder. The main goal has already been met, but there are a couple of interesting stretch goals set up, to include things like the addition of army management and giant monsters - Godzilla and laser armed frickin' dinosaurs, for instance. The funding options also let you pick up some nice bargains on the printed 1.1 rulebook when it comes out later this year.
You can find more information on Gruntz at Robin's website here - he's also got some very good painting tutorials and miniature review videos on there - and the Indegogo launchpad is here.