Gold Rush is a set of free wargames rules for late 19th century action in the Yukon.
rules
Giant Monster Invasion!
A table-top wargame for 2 or more players. It’s all about giant monsters, big cities, monsters in big cities, monsters thrashing big cities…you get the jist of it. The core rules are less than a dozen pages, and there’s also a bare-bones rules-lite version of it. Regular updates with new monster packs, some expansion packs, and so on.
Honoring cinema’s greatest giant monsters!
Mechbrawl Card Game
Mechbrawl is a free expandable card game. In it, you face off against your opponent in a giant, customizable war robot.
Starship Trooper Rules
Kurt Bowker has written a set of free wargames rules set in the Starship Troopers movie universe. I’m not sure where you would get the miniatures to go with these — perhaps Ground Zero Games has something that could be used.
HALO Combat Miniatures Evolved
HALO Combat Miniatures Evolved is a set of free wargames rules based on the HALO science fiction franchise.