FIST: Avalon is an arthurian hack of the cold war supernatural espionage rpg FIST.
The PDF is 16 pages, cleanly organized, with a slight OSR vibe. Everything is easy to read, and there's some appropriate public domain artwork.
In terms of departures from the FIST engine, the biggest mechanical changes here are the inclusion of Virtues, which require you to behave in certain ways during your adventures. Also you have a home base by default, plus a knightly order that you can progress through the ranks of.
The new Traits are nice and thematic, and the new progression system allows you to swap out Traits while keeping some of the old Trait's bonuses. This is flexible and dynamic and fits with the theme of knights changing and establishing themselves as they quest.
The game's scenarios, called quests, have a wonderful gimmick where they include both physical and moral obstacles, and this kind of guarantees that you're always thinking about what you stand for while you play. There's also a wide range of sample quests, each about three sentences long, and all of which feel easy to run off of the cuff.
Knights from FIST: Avalon can also be dropped into regular FIST games with a little bit of finessing, and don't overpower the existing game balance. They have a bit more growth potential than an average FIST agent, but are slightly more limited in their powers and technology and also by their Virtue. You could have a lot of fun just reverse Connecticut-Yankeeing a PC from this system into normal FIST.
Overall, if you like arthurian fantasy, or low-magic medieval settings, or courtly politics and heroic combat, this is a great FIST hack. It *does* require the base game to understand it, but it also fully transforms that base game in a really satisfying way. FIST: Avalon is well worth your time.
Minor Issues:
-This is a personal design philosophy thing, but I feel like recovering from being Broken or Tainted should give you two advancements to make up for the extra hassle. Arthurian knights had a tendency to kind of constantly lapse, get bested by their vices, and then try again, and providing two advancements turns the mechanic from one that the players want to avoid and the GM wants to force them to interact with into a mechanic where nobody feels the need to throw out their character if it comes up.
-Alchemist might benefit from a bomb/elixir carry capacity limit. Alternatively, "you start quests with X number of bombs and elixirs" prevents downtime bomb-farming shenanigans.
-Bastard and Foreigner thematically feel like Origin Traits.
-Patron gives -1 Creative. Should this be +1? Otherwise the Trait seems to be mostly downside.
-I would've liked to see a bit more about Castles, plus some example foes, but neither of these is strictly necessary to play or enjoy FIST: Avalon. It's a great hack, and I hope there'll be more supplements to follow it.