Coreheim is an updated rulebook for the venerable Games Workshop Mordheim system. I liked Mordheim (and its predecessor, Necromunda). I should get them out again to play.
Miniatures Rules
Napoleonic Wargames Rules
Paul Leniston offers a set of free wargames rules for Napoleonics. He and his gamer wife have been playing and testing them for many years.
World War III Rules
World War III is a set of free wargames rules for the period “1950 to armageddon.”
One Page Kill Team
One Page Kill Team is a set of free wargames rules for small scale skirmishes in the 40K universe.
Free Dust 1947 Rules
Dust Models offers a free digital version of their Dust 1947 rules.