Bonaparte is a set of free wargames rules for Napoleonic warfare. It’s in Portuguese, so your mileage may vary.
American War of Independence Rules
David Wareham offers a set of free wargames rules for the American War of Independence.
Firefly Outgunned WWI Microarmor Rules
Firefly Outgunned is a set of free wargames rules for WWII microarmor. They’re based on the old Firefly and Challenger rules sets.
Wild West Paper Buildings
Shadowwolf offers a nice set of paper models of Wild West buildings.
Minimal Melee Combat
Minimal Melee Combat is a set of free wargames rules designed to depict combat between sword armed adversaries.