'Fighter Duel' is a set of freely available variant rules which originally in 2018 used the aircraft data from the Avalon Hill WWII air combat game Mustangs, but from 2019 switched to using the data cards and later the single plane counters from the GMT Wing Leader series. It can also use counters from the SPI game Spitfire and the map from the Avalon Hill game Flight Leader. Fighter Duel covers combats between 2 to 4 fighters per side, and focuses on simple but realistic modelling of formation tactics, aircraft energy and situational awareness. The latest 2021 version of Fighter Duel Deluxe includes unique solitaire rules allowing any or all fighters to be placed under AI control. It is available here: https://boardgamegeek.com/filepage/180451/fighter-duel-deluxe