Questing Beasts is a campaign framework for FIST that reskins the game as being about a bunch of noble Arthurian holdovers in a post-apocalyptic wasteland.
The PDF is 10 pages, with a layout that's a little divided. The front half is stark black and white, with plenty of negative space, whereas the back half is more text dense and has some color in the illustrations.
Setting-wise, Questing Beasts is tasty. This isn't a rigorously documented worldbook, it's more about the vibe, but the vibe is the weirder parts of Arthurian legend crashing into a more modern post-apocalypse landscape, and this makes for a genuinely cool and fresh pulp setup.
Mechanics-wise, most of what Questing Beasts provides is new TRAITS. They're split into Merlin Type and Knight Type, giving a little variety to the sorts of characters people might play, and there's also a couple new Roles and rules to better mesh the FIST system with the changed setting.
Probably my favorite bit of the book is the Balin TRAIT, where once per session you can instinctively pick the wrong choice between two options---thus determining which one is wrong---but then your teammates have to stop you from making it.
Overall, if you like Arthurian stories, science-fantasy, and the kinds of pulp premises that could hold up a ten novel series in the 70s, definitely check this out.