Rogue traders of the 41st millenium
The idea for this game is more of a traditional, wandering-the-frontier type of space game. The idea is to take the existing Warhammer 40,000 universe, and emphasize the dynamic, conflicting nature. The Imperium isn't a monolithic, omnipotent entity; it is a mind-bogglingly huge amalgamation of fiefdoms, territory disputes, holy war, aliens, xenophobes, trade, persecution, misery and conflict.
The idea is that in your home games of 40,000, there's always Space Marines fighting Space Marines, Imperial Guard fighting Space Marines, etc. I'm saying this actually happens in the Imperium, as the space is too vast for a unified, bloodless union. Given that many authorities in the Imperium are functionally independent, such as the Inquisitors, Space Marines, and Lord Commanders of the Imperial Guard, and given that they don't always see eye to eye, such conflicts are inevitable. Usually they are quelled by the Administratum before any real damage to the Imperium can be done, but internecine conflicts spanning entire star systems are not unheard of. It's about as close to anarchy as you can get while still having a powerful central authority.
Painting the setting this way takes away none of the dark impressiveness of the 40k universe, while allowing some freedom for those who want to live in the in-between cracks of such a realm.
Contents
Cast
At least one player would need to be an Unlicensed Navigator, to allow the players some degree of freedom of movement. The players would be privateers, merchants, pirates, or any other group to whom mobility is of such a concern that they would risk their lives with every venture into the Warp. Aside from the Navigator, other players could be xenos, soldiers, space captains. Any kind of motley crew would be ok; aliens you've made up, ones from the Rogue Trader books, cyborgs, what have you.
The power level would more or less be up to the players, I think.
System
If I ran this, I'd probably use the WHFRP rules (again), because I like their capability for asymmetry, and the streamlined nature of combat. I might also use the Cyberpunk system. I'd probably ask for concepts from you all, make up careers that I think fit, and give you hints as to their exits. I'd keep rolling for stats, but allow players to pick which rolls go to which stats.
After some thought, it's apparent that rolling stats kind of sucks. Instead, we'll go with 77 points among the 7 primary characteristics in FRP rules, or 65 points point-buy in Cyberpunk.
Warp Travel
Given that warp travel is perilous and unpredictable, and given that the guide would be an Unlicensed Navigator, warp travel would be difficult.
I'm thinking that warp travel would involve some kind of game of chance, of the GM's choice, between the GM and the Navigator, with other players involved as the GM sees fit. Poker, Trivial Pursuit, craps, anything! And the more difficult the trip is, the more license the GM has to mess with the results of the game.
Setting
Were I to run this, I'd set it on the fringes of the Galaxy, where the Astronomican is too thin and unreliable for the real Imperial infrastructure to survive long. A frontier of sorts, where life is played looser, and the inevitable myriad transgressions the party commits against Imperial Law just by existing go unmentioned.
In exchange for this relative freedom, life is harsh. Resources are hard to come by, and people get desperate. The law is loosely enforced at best; those who enforce the law, being far from any dependable authority, are often lax or corrupt.
Worse, as the Astronomican flickers and grows weaker (as seems to be happening), tales of hideous Deep Space grow more common day by day. Some say that outside the Emperor's radiance lies Chaos, others say it is forces darker and more primal still. One thing is certain: travel through the inky depths is growing more hazardous. Every accident in the Warp, the story lost to the vacuum of space, creates a silence that crowds the edges of perception.