Letters of Marque and Reprisal is a set of free wargames rules for replaying battles in the age of fighting sail. It’s meant for battles where each player would control one ship, rather than a squadron or fleet. It looks perfect for pirate battles.
Miniatures Rules
Ancient Wargames Rules
Steve Burt offers a set of free wargames for Ancients Warfare.
Last Hussar’s World War II Rules
The Last Hussar blog has a set of free wargames rules for World War II. They’re a work in progress, so you’ll want to stop back by on a regular basis.
Alan’s Landship Game
Alan’s Landship Game is a set of free wargames rules that pits Victorians against Martians.
Reasonable Brom
Reasonable Brom is a variant of Larry Brom’s standard rules for the 19th Century.