Aggrotech is a subgenre of industrial music. If all industrial subgenres were flowcharted, aggrotech (alternatively "terror EBM" or "electro-industrial") would fall somewhere between EBM and powernoise. The word "aggrotech" itself is a portmanteau of the words "aggressive" and "technology", which describes this type of music perfectly. Aggressive technology. Yeeeah.
The majority of aggrotech artists got started in the late 1990s and early 2000s, but there are hints of it going as far back as the late 1970s. It all started, as these things do, with the earliest industrial music, or first wave: Throbbing Gristle, Ministry, Cabaret Voltaire, Front 242, Skinny Puppy, Nurse With Wound, Coil, Nitzer Ebb, Boyd Rice and of course Einstürzende Neubauten, covering the late 1970s to approximately 1988, when those inspired by the first wave started producing their own music.
There really weren't any subgenres of industrial music during the first wave, since there were so few performing it. These pioneers for the genre were, in their turn, inspiring new forms of industrial music, which became its subgenres and its subgenres' subgenres (whew). Today there are several different types of industrial music, and most of them overlap each other in various ways.
The word "aggrotech" was coined fairly recently to describe harsher, more synthetic sounds that didn't quite fit into the EBM pigeonhole. While many makers of industrial and EBM incorporate traditional instruments (i.e. guitar) into their works, aggrotech is completely synthetic (with the exception of the vocals, and even then they're processed and reprocessed to match the feel of the music), fitting comfortably between EBM, where vocals are universal and powernoise, which uses no vocals at all and is a fair degree harsher than aggrotech, all things considered. Some have described the sound as "militaristic".
In the early to middle 1990s, the second wave began, with such acts as KMFDM, X-Fusion, Suicide Commando, Terminal Choice, Hocico, Battery, Laibach, Feindflug, :wumpscut:, Leæther Strip and Genital A-Tech, though some (mostly people whose first exposure to industrial music as a whole was NIN) cite Nine Inch Nails' early, more aggressive works, too. All of these bands became known as "electro", "industrial rock" or "industrial metal" at the time. As the scene became more refined, classifying its members became much more specific. Aggrotech is probably the most recently-coined descriptor.
Prominent record labels include Off Beat, Alfa Matrix, Metropolis Records, Out of Line and Zoth Ommog, among many others.
Common themes among aggrotech songs are violence, politics (almost universally leftist), relationships (usually the acrimonious end of), rage, religion, technology, consumerism, pop culture and occasionally, not-so-subtle jabs at the scene itself. This is somewhat reminiscent of the 1990s shoegazer scene, dubbed by the British music press as "the scene that celebrates itself". This statement easily applies to aggrotech, with seemingly all the bands remixing their contemporaries' songs.
The scene has a large amount of quality music, legions of fans and bands that tour frequently. Almost every band sports the cybergoth look; lots of black clothing mixed with a primary/florescent accessory color added to compliment the black, creative makeup themes, impressively made-up hair (with lots of dreadfalls, tubing, spikes, and extensions, almost always in contrasting florescent colors), platform boots (Transmuters, Fluevog, New Rocks, etc.) and of course, the use of large goggles as an accessory worn near the hairline or around the neck. The popularity of the cybergoth style coincided neatly with the rise of aggrotech. Fans of aggrotech don't usually consider themselves goths, despite their cybergoth appearance, though some do. And on the other side of the coin, some goths don't consider themselves rivetheads or cybergoth despite liking the music.
The transition of club nights around the world from almost exclusively goth to almost exclusively industrial was made to cater to the rising population of cybergoths and rivetheads and their associated customs, while the traditionalist goth club and style went into decline.
Some of the (IMO) best bands include:
Some of these bands (Nachtmahr, Reaper and Suicide Commando especially) have rightly been accused of using misogynist lyrics and artwork, which is certainly not a good thing, but is also by no means widespread. On the other hand, some of these bands (Unter Null, Ayria and Angelspit, for example) are fronted by women.
... Among many others. If you'd like to hear some of this stuff, I recommend last.fm's aggrotech portal. As a genre example, try the song "Twenty6hundred" by Angelspit.