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 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 is a set of free game rules for duels between two wizards.
Hordes of the Empire is a set of free wargames rules for playing 19 century colonial battles. It’s a variant of Hordes of the Things (HotT), which itself is a variant of DBA.
Dale the Wargamer offers a set of Napoleonic Campaign Rules using the Risk board game.