American Civil War is a set of rules for 25mm figures in a 1:25 scale.
rules
Border Town Burning Mordheim Supplement
Border Town Burning is a free, unofficial supplement to the excellent, but abandoned, Mordheim, from Games Workshop. It’s got new rules, a new setting and lots of scenarios in a very professionally done format.
Shot and Sail Napoleonic Naval Rules
The prolific Jim Wallman offers a set of free wargames rules for Napoleonic Warfare called Shot and Sail. In addition to the pdf fo the rules, you’ll need the zipped graphics of ship cards.
Classic Battletech Rules
Classic Battletech is a free 24 page set of rules for playing the original game of giant robots on hex maps.
A Cast of Thousands Miniatures Rules
A Cast of Thousands is not so much a set of miniatures rules as a rules mechanic. It’s designed to allow you to play “cinematic games” where you set your own level of risk-and-reward.