For those unfamiliar with the Warhammer 40k setting, servitors are essentially cyborg zombies used for cheap slave labor by the Imperium of Man (the "good" guys). Convicts, underhive gangster scum, minor apostates, and other degenerates are vivisected and then lobotomized, with a primitive computer replacing the brain and various tools surgicallly substituted for normal limbs.
They are truly ubiquitous, found amongst all of the Imperium of Mankind's manifold bureaucratic subdivisions. This is especially true within the Adeptus Mechanicus, as the Tech-Priests of Mars are the only ones remaining with the knowledge of how to meld meatsack and metal.
Servitors may be found hardwired into the controls for a secondary weapon inside a Mechanicus vehicle, helping Astartes into their space marine power armor, or taking stenographic dictation for planetary governors. They are even responsible for cleaning and polishing the tens of thousands of miles of flooring within Imperial Navy warships!