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.
Phantoms is a set of free wargames rules based on the old Avalon Hill “Mustangs” game. It’s for playing air combat games from 1960 to present. The link is to the deluxe version with all of the updates, data cards and scenarios.
Vietnam Air Fury is a set of air combat rules based on the earlier Space Fury Rules.
Air War 1917 is a barebones — and free — version of Wessex Games’ AirWar: 1918 biplane combat rules.
Luft ’46 is a site that offers a wealth of information on aircraft projects that the Germans had in line is World War II had lasted a year or more longer. Fascinating stuff. I’d like to see some of these show up on a wargames table.