Net Epic is a set of free wargames rules based on the old Games Workshop Second Edition Space Marine.
Miniatures Rules
Little Lambent Meteors
Jim Wallman’s Little Lambent Meteors is a set of free wargames rules for 18th Century riots, using 15mm figures.
Road Warriors rules
Michael Taylor has written Road Warriors, a set of free wargames rules that uses Matchbox cars for games set in a post-apocalyptic future, ala Mad Max.
1 Page Napoleonic Skirmish
The Jackson Gamers have these free wargames rules for Napoleonic skirmishes. The best part: the rules are just one page long.
Ares Fantasy Skirmish Demo rules
Majestic 12 games offers these demo rules for their Ares fantasy skirmish miniature wargames system. They explain:
ARES: Miniatures Wargaming System is a complete skirmish-level fantasy game. But it is also much more. The flexibility of the system allows players to use any wargaming miniatures in their collection. Over two dozen sample figures are detailed in this book, but the real strength of ARES is its figure creation system, that encourages players to use their imaginations — which is the way it should be! Also included is a fully-customizable magic system, providing players with the opportunity to design their own spells for their troops.