Skank Games offers Warlord 2085, a set of free wargames rules for fast play science fiction miniatures.
Miniatures Rules
Strange Aeons 18th Century Modifications
Strange Aeons is a commerical rules set, but if you already own it, you may be interested in these free modifications for playing in an 18th Century setting.
A Splendid Victory ECW Rules
A Splendid Victory is a set of free wargames rules for the English Civil War. They’re designed for 28mm figures, but the basing system is flexible.
Pigs and Glory: The Viking Sagas
Pigs and Glory is a set of free wargames rules for Viking Saga Campaigns. It is designed to give some context to period battles.
1862 Campaign Rules
1862 is a set of American Civil War Campaign Rules designed for Johnny Reb, but which could be used with any miniatures rules set.