If you didn't know, The Retired Adventurer has some lovely rules changes to Stars Without Number to play in the grim-dark-grimness of the Imperium of Man. The rules as is are tailored kind of towards Dark Heresy play, which is low-level inquistors out exploring the universe, which I find is a perfect level for SWN and the best way for Warhammer players to really "get into the shit."
However, for the next few posts I'm gonna elaborate on the character options to make the options a bit more inquisition, and Imperium, inclusive. This means I'll cover the mutated Abhumans, Space Marines (Grey Knights and the Death Watch, specifically) and the Adeptus Sororitas. But first, the Abhumans!
Ogryns are huge abhumans, often employed in the Imperial Guard as heavy weapons troops. Groomed on numerous death and hell worlds, an ogryn is designed for only one thing: survival. They rarely win any debates, but rumors tell of ogryn easily besting some Space Marines in unarmed combat.
Ogryns must have Strength 14+. Ogryns can literally eat anything for survival, though poisons still affect them. They are automatically trained in Survival.
Ratlings are small, loud and annoying creatures with hairy feet and bad attitudes. Despite this, the Imperial Guard can rarely find a better pathfinder or sniper than a ratling. Entire companies of ratling snipers have single-handedly won campaigns, only to later go off and get piss-drunk. Despite this, they are useful allies.
Ratlings must have a Dexterity of 14+. Ratlings have almost preternatural aim; they don't suffer the normal -2 penalty to shoot beyond normal range.
Fairly rare abhumans, beastmen have features of, well, beasts. The most common features are goat-like, with the beastmen often looking like satyrs with goatish heads. Beastmen are fairly maligned, more than any other race, as many believe them to be straddling the lines of chaos. Ironically, beastmen are some of the best at tracking down corruption.
Beastmen can not have a Charisma of 9+. Beastmen can actually sniff out Chaos on a successful Perception roll, being able to smell the evil taint. Beastmen also can head-butt with their horns, dealing 1d6 damage.
Squats are a nearly dead branch of abhumans, nearly completely wiped out by the Tyranids. Those that remain are usually in the Imperial Guard serving as mechanics, pilots and so on due to the squat's natural affinity to technology. Short due to their lives on high gravity worlds, they appear much like humans save for their stature and general harriness.
Squats must have a Constitution of 14+. Squats are trained in Tech/Any and Vehicle/Any.