If there's one thing that unites the warring tribes of the Warhammer 40k fandom, it's this - unlike other sci-fi fans, none of us actually want to live in the universe we're obsessed with. With trillions of humans in the Imperium of Man, being reincarnated into the 40k universe all but guarantees that you're not going to be a Space Marine - you're going to be one of the robe-wearing serfs in the background of the paintings, with blindfolded eyes and a candle on your head or a book chained to your face. But if you do want to find out what that might be like, there's a new free indie RPG from talented designer Zedeck Siew that lets you do just that - it's called Chapter Serf.
This isn't an official Warhammer 40k RPG, but it's very well put together - a 75 page PDF that has full rules, 36 different weirdos to play as, a fully detailed Space Marine voidship called the Warmask of Gloriana to explore, complete with an open-ended scenario that's ready for you to stumble into.
You can download Chapter Serf for free from Siew's blog.
Siew is a very active indie TTRPG designer (plus a journalist, editor, and critic) who can pack maximum vibes and playable content into minimum text. Just reading the book is a pleasure - though if there's any chance you're going to join a game as a player and not a GM, stop reading before you get to the descriptions of the ship and the NPCs. Going further would spoil the fun.
The game uses a very lightweight dice system to resolve conflicts. Stats are generated from 3D6 for a range of 3-18, and if there's ever a question about whether or not an action succeeds you'll try and roll under it on a D20. Combat is simple and lethal, and the rules are generally designed to stay out of the way: the game's focus is the world that your miserable characters exist in, both materially, and culturally.
The Gloriana is divided into seventeen large zones, from the Bilges up to the Navigator's Spire, and it will take your characters literal days to move from one end of the ship to the other. Short characterful descriptions reveal locations and events that could logically exist on a Space Marine vessel, but which would never be the focus of a Warhammer 40k book: the corpse-processing Circulum, which renders down dead crew into fertilizer for the Myco-farm; a fishmonger in the crew habzone selling blind eels caught in the bilges; a gunnery crew practicing firing drills.
There are just five Space Marines on board the ship, and the game warns you while you can petition them for help, "there will be maximum carnage and collateral death". If they're ever onstage, you must bow and preferably kneel, speak only when spoken to, and do anything they tell you to do.
Most of the time you'll serve different petty lordlings from among the other serfs. These each have their own agendas, opinions, desires, and domains. The Seneschal wants to see conflicts among the crew resolved without bloodshed, and can assist you with mundane resources and useful but ordinary services; the Chief Enginseer wants rare tech and to gain control of more of the ship, and can loan you powerful weapons or the use of a small voidskiff to travel freely between zones of the huge ship.
The adventure kicks off with a randomly chosen assignment from the Seneschal, a thread that once pulled will uncover an irresolvable conflict between different members of the crew, or a potentially fatal systemic failure growing somewhere in the bowels of the Gloriana. Can you fix it? You're probably not equipped for the job - before this tasking, your character might have been a hive city chimneysweep who grew too tall, responsible for trimming a Space Marine's beard, or an asteroid miner who won a lottery and escaped from one life of sunless toil and into another.
I haven't played Chapter Serf yet, but oh boy do I want to. Playing as underqualified rubes with impossible missions in an absurdist hierarchical society is exactly the same setup as Paranoia, the original comedy RPG, and that game sings to this day. As a fan writer making a non-commercial project Siew isn't limited by canon, letting him sharpen the satire, absurdity, and pathos of the situation. And he's free to include wild shit we haven't seen in 40k since the 80's - like a mutant with an entire arm in place of his penis.
If you'd like to join a community of fellow weirdos who would definitely be crushed for irreverent behavior if we lived in the Imperium of Man, you're most welcome in the Wargamer Discord. Also, if you're interested in the aesthetic of the pathetic and depictions of fringe existence in wargaming, I recommend you check out the documentary The Grim and The Dark: see my film review for more details.