There are three main sources on robots in GURPS: THS has some (dubbed cybershells), 3e’s Robots has several more and a whole design system, and 4e Ultratech has some more.
From page 121 on, THS provides a total of 14 different robots. Worth mentioning are the Buzzbot (just like present day’s quadrocopters except in a helicopter configuration), a mini-manipulator robot, a reconfigurable spider- or worm- or arm-bot, and my personal favourite, the mobile helmet.
Militarily, two cybershells are offered: The RATS, a 250lbs four-legged ground-combat cybershell mounting a 10mm PDW and mini-missile pod, and a UCAV, an 800lbs hyper-agile fighter armed with a 15mm emag cannon.
A few more robots are scattered throughout the different THS supplements, but the majority is there.
3e’s Robots has as many different robots as you’d like, seeing as it has a whole robot design system (which can also design battlesuits). It also quite a few sample robots. Combat robots, farming robots, exploration robots, VTOL robots… you name it.
I’ll definitely will be spending another post to construct a few example robots.
4e’s UT features two combat robots (each available in several different configurations): The combat android and the heavier Warbot. Both cost roughly the same, but the latter is definitely optimized towards combat, featuring consistently higher armour (DR75 vs DR45), three weapons, but also massing half a ton. The Warbot also exists in a submarine or VTOL configuration.
It somewhat suffers from the same issue as THS: While there are a few nice options, I cannot build new robots. Well, I can build them as characters, but that doesn’t give me cost, mass, or capabilities.
THS, 3e Robotics, and 4e UltraTech all feature Microbots (and the latter two have nanobots available). These are insect- to dust-sized robots which cooperate and and network, therefore achieving somewhat intelligent behaviour. They are featured in the introductory blurb of THS (“Fiercely engaged by dense swarms of black-market Wespe and BlutMuzak microbots, the first assault section dissolved moments after taking the docks.”).
However, I don’t believe they’ll work in a military context. Why? Communications. We know that microbots are at most flea-sized. A flea masses roughly 1mg (1/1000th g, or 1/500,000 lbs). If we fit a radio in there (assuming half of that mass is taken up by the radio), and it scales linearly down (it doesn’t, check out Vehicles 2e p. 48), this will have a range of 0.02y (approximately 2cm or the width of two fingers). That might be sufficient for intra-swarm communication.
However, we can build a radio jammer: A medium-range TL10 radio jammer masses 0.25lbs, costs $50, and has a range of 5 yards. At a distance of 1 yard to the swarm, communication becomes impossible at closer than 4mm (0.004y) intra-swarm distance. If we increase the mass of the jammer to 2.5lbs, it has the same effect at 10 yards.
Accordingly, any macro-scale robot (or soldier) can simply mount a jammer to create a safe bubble into which swarms cannot penetrate without losing their coordination. This means their military applications are significantly limited.
Somewhat shorter, the only decision I’m taking today is that microbot swarms are not used militarily (because they are easily countered). Militarily, I’m fairly sure we’re going to see battlesuit-armoured human soldiers coordinating squadron- to platoon-sized robotic forces and will probably build some in the next post.