Here's a set of rules that my club has been enjoying recently.
It's a really fast playing mass battle ruleset for 3mm-15mm miniatures called Panzer 8. The author has adapted it for nearly every genre, including sci-fi which we play. It's basically a way to get a ton of units on the table for a fast-moving game that retains just enough detail to be a satisfying game. The points system is easy to break, but group of cool headed players can usually arrange suitable force lists for an enjoyable scenario. After playing it quite a few times, we came up with a few house rules. Since the ruleset is only two pages long I decided to go ahead and rewrite it a bit for clarity and add our rules. The result is attached below as well as a force list with points.
Though it's been pretty extensively playtested already, I'd still be curious to hear what folks think of it.
Though many folks like to write their own ruleset, it's been our experience that usually a good ruleset already exists and sometimes it just needs a few tweaks.
We've been playing it in 10mm using rebased figures from the Mechwarrior clix CMG, though one member uses Epic
40k Titans. I've posted a few of our AAR's here before, but if you can see the game in action here:
http://chicagoskirmish.blogspot.com/2013/01/mech-attack-and-panzer8-for-10mm-sci-fi.html
http://chicagoskirmish.blogspot.com/2012/09/trying-out-panzer-8-for-quick-play-sci.html
The original home of Pz8 and all it's free variants is here:
http://panzer8.weebly.com/links.html
Enjoy