Incursion is a Roadside Picnic/Stalker spin on FIST and MOONGRAVE. Notably, it twists the formula by having the Zone be mostly scavenged out, but one big prize still remains.
The PDF is 27 pages, with a simple, unornamented, technical manual style layout. It's easy to read and uses white space well, but there are no interior illustrations.
Mechanically, Incursion deviates from FIST's loose structure and saturday morning cartoon tone. It's a gloomier, more desperate game, and it relies on specific mechanical frameworks to reinforce that.
Doom is a new resource that accumulates during the game's first phase, and imperils you later. Phases are now a thing. The game consists of a trip out into the Zone, and a trip back. Each trip takes three days, and encounters and camps are evenly spaced between them. There is a concrete end point, and when characters die their players can't reroll and come back in.
The writing of Incursion is really solid and direct. I don't think I've seen many games take such a no-nonsense tone, and it works for the material. You could just read this game and still feel like you've played it, and that's impressive.
However, in terms of gameplay, this *is* still a playable thing. There's a small assortment of FIST TRAITS, as well as new INJURIES that debuff you after you receive them.
For GMs, there are roll tables to generate encounters on the journey across the Zone. There's also plenty of advice throughout on how to run it, and a deep breakdown of the philosophy of the game. It's all a good read, and worth not skipping.
Overall, if you like games that lean on tone and atmosphere, that have heavier and bleaker vibes, and that explore their characters and the landscape around them, I'd strongly recommend this. It's a great FIST hack and an equally solid standalone and it has a lot that's worth reading even if you aren't going to run it.