The Regular Army O! is a set of free wargames rules for battles of the 19th Century. It’s of a rather nebulous scale, although there is a reference to “regiments” in the rules. Mediafire rules link.
rules
Flint and Feather Basic Rules
I played Flint and Feather at a local con last fall and thought it was quite interesting. It’s a skirmish game about the “Heroic Age” of the Great Lakes First Nations. You can get the basic rules here.
Brickquest Miniatures Rules
Brickquest is a set of free miniature wargames rules for dungeon adventures along the lines of Heroquest or DungeonQuest. The catch here is that it uses Lego guys.
Combat Action Wargames System
Combat Action is a very complete universal wargames system by Fabio Fontana. He writes:
Combat Action is a strategy game of small scale conflicts. It can be used to represent skirmishes with a dozen models per side up to larger conflicts with multiple squads, vehicles and support weapons. The system presented within this book comprises two levels of detail, a simple system for small scale games where each model on the battlefield is a separate unit, and a more complex layer which adds optional rules to govern targeting, simulate chain of command and allow larger engagement of forces.
The point system will allow you to design any creature, vehicle or model you like, and field any model you create on the battlefield.
The site also has playscreens, scenarios and a complete world background.
Tabletop Titans Superhero Game
Ed Walker has written a set of free wargames rules called Tabletop Titans. He writes:
BAM – POW – KAZOWEE. These are the sounds of super heros in action. Who could forget the wild brawls we all envisioned while reading our favorite super hero comics? Tabletop Titans is a game of miniature combat where players create super heros to do battle. Designed to be played on any tabletop or with one of the many types of terrain systems on the market Tabletop Heros provides all the rules necessary to create a unique super hero and pit it in combat against other superpowered beings. Tabletop Titans uses the ACTION combat system.