DMZ - A FATE Core Space Opera
Nanotechnology is simply transhuman technology that operates at scale of 1 to 100 nanometres. This can range from the creation of molecules at that scale, to self-replicating swarms of machines capable of dissembling matter and reshaping it into any form.
Nanotech is largely the preserve of level 4 or higher civilizations, though some lower tech societies have access to relic nanotech. Most nanotech across the DMZ is not self replicating, and takes the form of a hive, a small machine that stores the matter to produce and replenish a swarm of nanomachines. Most of the time, these hives and nanomachines have a specialised purpose – many transhumans from advance societies have a small implanted hive that produces nanomachines that circulate through their bodies, curing diseases and repairing damage at a cellular level (so-called medichines). A utility fog is a hive which produces a general purpose assembly swarm.
The single greatest risk associated with nanotech is the risk of a grey goo scenario – where a self-replicating nano-swarm gets loose and converts all the surrounding matter to more nanomachines. Theoretically, a swarm like this could destroy a planet or even a solar system. Most nanoswarms have a inbuilt limits to prevent such an occurrence.