Tournament: Pageantry and Pain is a set of free wargames rules that allow players to guide a knight’s retinue through a tournament.
rules
Large Scale Civil War Battle Rules
Large Scale Civil War Battles is a set of free wargames rules where one base=1000 men and an inch=100 yards.
Inquisitor Rules 40k Universe
Inquisitor was game produced by Games Workshop set in the Warhammer 40K Universe. Curiously, it used 54mm figures.
The game is out of print, but a rules archive is at the link.
Dino Hunting Rules
Here are a set of free wargames rules for conducting a Dinosaur Hunt.
A Fistful of Honey Cowboy Bear Rules
Eureka Miniatures offers a one-page set of rules for playing wild west shootouts with its teddy bear cowboy figures.