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.
MIG Alley Ace are rules for modern aircraft combat from 1945 to the missile age.
Contre Les Viets is a Vietnam variant of Arty Contliffe’s Crossfire. You need the original rules to play.
Incoming! is a set of modifications for using Arty Conliffe’s Crossfire game for the Vietnam War.