Book 3 gives a couple of vague hints: you're dealing with an antimatter energy technology, fully sapient robots, ships armed with disintegrators.
MegaTrav
Referee's Companion gives a few more detailed clues:
At TL18 there are disintegrator rifles, disintegrator cannon for tanks and artillery, and disintegrator weapons for ships. They're supposed to be extensions of damper technology - in this case they, "disrupt the strong molecular attraction that holds matter together, causing an object’s molecules to fly apart." Easiest to think of them as creating a field that lowers the boiling point of matter in the affected area to basically nothing, causing the matter to spontaneously turn into a gas. There are also dampers, basically a field that prevents that effect; there are personal dampers as well.
If you're not playing MegaTrav, you'd have to make your own rules up on how they work. Rifles might project a beam that disintegrates anything on that line, with armor being of no help at all; or they could create a small spherical node of a certain radius (maybe man-size, maybe fist-size, depends on how survivable you want it) that disintegrates everything inside that sphere, or they could act like a good ol' Star Trek phaser, a beam that reaches out and induces a spreading disintegration bound by the dimensions of the object and the power put into it. Canon might disintegrate all matter in spheres as big as the area affected by an artillery shell - or might just be the Star Trek disintegrator writ big, with the ability to disintegrate ten or a hundred times as much matter. Starship weapons range from the canons to spinal mounts that can make a whole ship or a city block go bye-bye.
(Keep in mind that what you're basically doing is suddenly turning an amount of matter from a solid, at about the density of water or more, into a gas occupying the same volume at 1000 atmospheres. The results can be explosive and potentially damaging to the lungs of those nearby depending on the mass disintegrated. Little disintegrations are safer to bystanders - and the firer: a big dramatic whole-body disintegration could kill bystanders within 4 meters and knock people off their feet 10 meters away. Making a city block go poof is likely to be very devastating to the neighboring blocks out to a
radius of ten city blocks or more.
Star Trek does not seem to be aware of that. Of course, you could decide they turn into a liquid instead - less destructive, but definitely more gory.)
Also common are neural weaponry and neural shields: think phasers set to stun, and a defense against same.
Power is antimatter-based. That doesn't actually sound like an improvement to me since they either need a source of antimatter or need some other source of power to make the antimatter, but I imagine it does make fueling things a bit easier - once you get past the containment business and the realization that your fuel could kill you and everything within several miles. Maybe they just use it in space.
Robots and computers are fully sapient and self-aware: your computer is very literally your friend - or maybe your boss. If you tell him that he's just a machine, he's likely to remind you that you're still governed by the same fight-or-flight instincts and reproductive urges your fish ancestors came out of the seas with, and it took you a year just to learn how not to wet your pants, while he can adjust and improve his own programming as he sees fit. He'll also remind you that he votes. (And if he doesn't, you might want to worry about the underground robot liberation movement.) Flesh-people work mainly because it's boring not to.
Starships are self-aware and crewed by robots. Why put a human in needless danger when the machines can survive and recover from anything short of a brain shot - and can download a backup of themselves elsewhere just in case that one dies?
Communications: why carry a cell phone when you can have one permanently implanted behind your ear that responds to voice commands? For that matter, why bother with a computer screen when you can have that same chip feed you visual and audio data directly from the computer? Carry the internet in your head. Be IN the video-game. Hey, in a couple more tech levels, maybe we can do away with speech entirely and just communicate brain to brain. The Singularity is due in a few generations.
Medicine: they can cure anything up to and including death, if they get the body quick enough. They can cure death if it take a little too long, too - it's just that they have to program in a new personality since that one is too damaged. After all, you only really need him to say things like "What," "I don't understand" and "Where's the tea?"
