This is my first mod, so go easy on me
I do not own Warhammer 40K or anything in it, it is the property of Games Workshop, blah blah.
Also I don't own a few metals in the mod that Blizzard though up of, etc.
Races:
Imperium (Humans), with Ogryn, ratlings psykers and space marine castes. They use lasguns, bolters, chainswords and power weapons. They also have flak armour and power armour.
Eldar equipped with shuriken weapons that fire tiny metal discs and stronger power weapons. They can make wraithbone and use wraithbone as their main material.
Chaos, with bloodletters and chaos minions (cultists). They use corrupted weapons. Chaos Spehss Mereens will be added soon.
Orks who have Orky weapons and armour. They can make Ork Scrap, a metal slightly stronger than steel, without using fuel. They only have lungs and a heart, and they feel no pain so are difficult to kill.
Tau with Kroot castes. They use pulse weapons and kroot use kroot staves.
Dark Eldar are to be added next release.
Each race has their own armour types.

Very basic alpha, with entities still in the works along with weapons and materials. Vanilla creatures are still in.
New materials: Metals from the Bridge mod, a few new metals from Valikdu's Tyranids mod, wraithbone, plasteel and plastic. Also: Flamerfuel, a metal which ignites below body temperature. Handle with care, especially in hot climates.
New creatures: Valikdu's Tyranids, a few squig variants and a particulary vicious new Megabeast, the feral greater knarloc.
Crude oil has been added so you can make plastic and flamerfuel.
Psyker weapons are very powerful.
The mod's quite messy at the moment, I'll sort it all out before next release, and that's a promise.
I'd reccommend just using it for arena mode and experimenting. The next release will be quite soon and probably won't be old save game compatible.

Thanks:
AWdeV on the Taleworlds forums for the idea of the shuriken discs,
LucasUP for his excellent utility, the Lazy Newb Pack,
i2amroy and Greiger on the Bay12 Forums for answering my questions,
Valikdu for his excellent tyranid bodies,
and Aramco for his bridge of power metals.