Invaders

The Invaders are a group of highly advanced aliens that assaulted Humanity with no provocation in 2050. Their favoured method of attack is landing giant pyramid-shaped atmosphere processors between multiple popuation centres and using them to pump trillions of tons of nanorobots into the atmosphere, killing everything nearby instantly before spreading out to gradually kill everything else. This tactic was stopped on Earth by simultaneous deployment of every Fusion warhead on the planet to America, 'glassing' the continent and killing billions, but stopping the spread of the gas with their concentrated bursts of EMP (not that this was known at the time).

Over the next hundred years, the Invaders were fought doggedly by an ever-dwindling group of human resistance which were led by several select humans who found themselves enhanced by the Invaders' nanorobots to the level which they could effectively fight back. Sometime in 2150, the Invaders withdrew and left Earth as quickly and inexplicably as they had arrived, leaving an Earth devastated by a war that had left 95% of the population dead, and almost as much of the landmass a radioactive, uninhabitable shell.

Invadertech and Chimeratech
For all the Invaders took from humanity, they have undoubtedly left a few things which have aided in the rebuilding process. These new technologies come under two types; Invadertech (technology that is purely of Invader design) and Chimeratech (human technology enhanced with Invadertech techniques, or vice-versa). Some examples include;
 * 侵入者 (Chimeratech). The Intruders are a combination of Jhinan battle armour and Invadertech propulsion systems. While they are incapable of flight, they can power a heavily armoured human along at the same speeds as a car.
 * Jetstream Boosters (Invadertech). The Invaders are the unparalleled masters of the air and, while humanity has yet to get back to flight, it has at least put the engines in some of the more robust vehicles, allowing for boosts of speed at little cost to handling beyond what the human mind can process.
 * Lumière-Dure (Chimeratech). Created by the French from Invadertech force field technology, Lumière-Dure (Hard Light) projects a force field that heats up, causing a source of light and heat that can be bent and shaped at will. While this has been used in weapons (mostly swords and pistols), it is almost as commonly used to make glorious sculptures.
 * Nanogas Generators (Invadertech). While most are deactivated, there are still the occasional working generators of Invadertech nanorobots. Without direct Invader control, this nanogas goes inert after a few seconds, but it can be collected by unscrupulous humans to be used as a weapon before that happens. Most humans wouldn't think of using such a terrible weapon, but enough do to make it fairly common.
 * Nanogeneration (Chimeratech). A technology pioneered by England, Nanogeneration involves using Invader nanorobots to transform the molecules of any matter into any other matter. Using this technique, waste can be turned into sustenance (if not what anyone of sound mind would call food), plastics can be turned into metals, and the dust in the air can be turned into bullets. While all but the most powerful nanogenerators can only hold together for so long before turning back into dust, it's usually long enough for any sustenance to be derived from food, or for a bullet to kill something.
 * Partikel-Fusion (Chimeratech). An odd technology of the Germans, that wasn't based on existing Invadertech, but rather inspired by it, Partikel-Fusion (Particle Fusion) is Cold Fusion, only miniaturised, causing cutting beams that strip away what it touches on a molecular level. This is primarily used to make precision tools, but, like the rest of the world, it has been weaponised, mainly into axes and rifles.
 * Reaper Nanorifle (Invadertech). The sole weapon of the ground forces of the Invaders, the Reaper fires streams of nanorobots that furiously devour whatever they touch before deactivating after a second or so, causing targets to die horribly, screaming in agony. So rare it has obtained the status of myth among some communities, it is statistically improbable to even see one, let alone own one.
 * Военачальник (Chimeratech). While many cultures spent their time trying to rebuild, Russia descended into multiple warring states, caring more about killing each other than allowing humanity to restart. One upshot of this is the Warlord Combat Drugs, created by lacing plants with deactivated nanorobots to create a temporary boost to Transhuman potential.