Fubar is a good looking one page set of modern and science fiction rules.
rules
Air War Korea Rules
Air War Korea is a set of free wargames rules for introductory level air to air combat in Korea. The author says Air War-Korea is highly suitable for group play and can be learned quickly, with only a few pages of rules. The rules include all markers and templates needed to play the game.
Battle of Britain Rules
Battle of Britain is a set of free wargames rules for operational level games. The authors write:
This is a fast playing operational level game about the German air raids over England on August 8th, 1940. Designed for group or convention play where players are in charge of the various sectors or Luftwaffe raids and it can be completed in a few hours. This PDF includes the rules, a map, markers, cards, and aditional materials needed to play the game.
A Meeting of Hosts
A Meeting of Hosts is a set of rules for simple ancient wargames with toy soldiers by Ross Macfarlane, inspired by Joe Morschauser and Don Featherstone.
A Spot of Friendly Wizardry Game
A Spot of Friendly Wizardry is a set of free game rules for duels between two wizards.