Murder servitors are murder servitors. Lobotomized murder cyborgs.
Skitarii are the Mechanicus equivalent of Imperial Guard - soldiers with tons of bionics but still capable of thinking.
Thallax is Mechanicus Space Marines. They are permanently fused into their Power Armour (the Lorica Thallax), but also still capable of thinking. While they do still exist in WH40K, the secreft of their production seems to be lost.
Legio Cybernetica uses robots - however they weren't AIs and they weren't biological, sort of really advanced unmanned vehicles. Those were really heavily restricted and basically useless without a Mechanicus imputing commands. However, even if they weren't actually thinking, they started to show signs of intelligence, like a lot of things (because in WH40K you can make shit happen just by believing hard enough). This wasn't cool, but even then Horus Heresy happened first, and nearly whole Legio Cybernetica fought on the traitors side. After it, they ended up in Eye of Terror (Blight Drones bear striking resemblance to one of the flying robots, just with more Papa Nurgle on it), and whatever remaining cohorts that remained loyal got royally buttfucked by laws and stuff so they aren't really a big deal in WH40K.
Of course, this was just an explanation why they aren't here, while in reality it was because GW was too lazy and too busy making Ultramarine Mary Sues. Now, with the focus back on the cool aspects on Wh40k, Legio Cybernetica is again a thing both in WH30K and WH40K. They're fucking cool, basically everything from fully robotic Guardsmen through Space Marines and Dreadnoughts to Imperial Knights and (supposedly) Titans.
So, TL;DR - respectively horror murder machines, cyborg Guardsmen, cyborg Space Marines and army of remotely controlled death drones.