Only War
"...in the grim, dark future there is." -Yoda
The latest entry in Fantasy Flight Games's Warhammer 40,000 Roleplay product line, in which players take the role of Imperial Guardsmen. Currently a pre-written adventure and pack of characters has been released, and the Beta edition of the rules is being sold online for $20 as well. This includes much of the rules, but no fluff at all.
Players roll up Guardsmen from different disciplines within the Guard - heavy weapons specialists, pilots/drivers, techpriests, Commissars, and so on. Each player also gets one or possibly more background NPC helpers, referred to as Comrades. These Comrades serve as extra hands, ablative wounds or even something for the Commissar to BLAM.
The vehicle rules look promising, and seem more streamlined than Rogue Trader's.
/tg/ has since created the 1st Membranes, a fan regiment made using the creation rules found in the Only War beta. They are made primarily from Psyker stock, and as a result are a regiment of gibbering, schizophrenic and/or awesome troopers who, when confronted with Orks, will either scream at the things coming out of the walls or mow down hordes of greenskins with mind bullets.