Half-Life begot the mod Natural Selection, which begot standalone sequel Natural Selection 2, which together with NS1’s Combat mode incestuously begot NS2’s Combat mod, which now begets standalone game Natural Selection 2: Combat. It’s all a bit like Chronicles with assault rifles.
Faultline Games are taking their Combat mod standalone, they’ve announced, expanding and polishing it up as one would expect. Combat’s a murder-oriented version of Natural Selection, focusing on the asymmetric humans vs. aliens FPS combat while doing away with RTS-y bits like resource-gathering and commanders. It also splashes in RPG-y levelling, with murder-earned skill points unlocking new weapons, tech, life forms and whatnot.