Universal Combat System is a set of free wargame srules described by the authors of being for “any number of players in an infinite amount of settings.”
Advanced Wargames Rules is actually a fairly simple set of generic rules
Serious Lemon’s Full Command is a set of free wargames rules:
for simulating battles all the way from a skirmish level with a handful of individual models through to full scale war with units totalling hundreds of miniatures.
Full Command has been designed to be setting and scale agnostic. It can be used to play 28mm skirmishes in an ancient setting to 15mm ranked warfare in a medieval fantasy setting to a 32mm heroic squad based battles in a far sci-fi setting.
Full Command is being released under Creative Commons (Attribution-ShareAlike) to allow maximum flexibility and freedom to gamers everywhere. Always wanted to play that game where Zombie Alien Pirates are battling the Savage Ape-Men on Mars? Grab the core rules, whip up a setting module with a couple of factions and you’re away.
Politics By Other Means is a miniatures matrix game designed to cover all eras.