Here’s a set of rules for American style football games.
Rules: Modern
Low Level Hell
Low Level Hell is a set of free wargames rules for helicopter actions in Vietnam.
Vehicular Pursuit Rules For Fistful of Kung Fu
The Osprey Rules A Fistful of Kung Fu 
Army Men Skirmish Rules
Army Men is a set of free wargames rules designed for use eith the classic plastic army men.
Ambush Guerrilla Wargaming Rules
Ambush is a set of free wargames rules for guerrilla warfare 1960 – 2000.