Few technological breakthroughs are as misunderstood as nanotechnology. Broadly defined, "nanotechnology" is the use of machines the size of a nanometer (one millionth of a meter, larger than a molecule but smaller than a cell).
Nanotechnology deals with the mechanics and engineering of small groups of atoms. As such, it blends into chemistry, which deals with chemical reactions between groups of atoms and microelectronics, which deals with how groups of atoms behave in an electric field. In realities where magic operates, nanotechnology also blends into pseudo-flesh animation, which deals with how atom-sized demonic creatures operate.
Nanotechnology was first described in the second half of the Twentieth Century, and early attempts at nanotechnology were common by the Twenty-First Century. These early steps were almost entirely based on the design and fabrication of nano-scale materials such as fullerene (buckyball) tubes and spheres. Although few realize it, this early nano-technological revolution was responsible for many of the inventions that so changed the 1990s and onward. For instance, lithium-ion batteries, and therefore cell phones, portable computers, and ultimately cheap electric cars all relied on nano-scaled materials.
It wasn't until the 2020s that the next stage of the nanotechnology revolution bloomed. Nanoscale materials had wonderful, unique properties, but were essentially static. Soon it was discovered that atoms could be used as the basic building block for sub-microscopic machines. These machines could generate and store power, fabricate and compound raw materials (and without pollution or external energy), and form the building blocks for a whole new generation of portable products. A fifty square foot, ten atom thick sheet of nano-factories could easily power a house. A ton of free-range nano-factories could recover the miniscule amount of gold (or uranium) dissolved in sea water. Nano-components were even used in cell phones that were for all practical purposes tattoos.
On the other hand, masses of nano-disassemblers could dissolve nearly anything. The nano-cannon was but one crude example of the destructive nature of nanotechnology.