Nanorobotics is the technology of creating machines or robots at or close to the scale of a nanometer (10-9 meters). Nanorobots (or Nanites) are typically devices ranging in size from 0.1-10 micrometers and constructed of nanoscale or molecular components.
The first working nanoscale robots were created over 200 years ago, but have only recently, within the last 50 years, received widespread application.
The first useful application of nanomachines was in medical technology, where they were used to identify pathogens and toxins from samples of body fluid and destroy them. Later early nanorobots were used in the detection of toxic chemicals, and the measurement of their concentrations, in the environment.
Since nanorobots are microscopic in size, it is usually necessary for very large numbers of them to work together to perform macroscopic tasks. These nanite swarms, both those which are incapable of replication and those which are capable of unconstrained replication in their intended environment, are able to accomplish a wide range of goals.
Medical nanotechnology is typically injected into the patient to perform treatment on a cellular level. Such nanorobots intended for use in medicine typically do no not replicate, as this would needlessly increase device complexity, reduce reliability, and interfere with the medical mission. Instead, medical nanorobots are manufactured in carefully controlled nanofactories in which nanoscale machines are solidly integrated into a desktop-scale machine that builds macroscopic products.
There are many uses of nanorobots, such as defensive units used to "heal" armor, and also repair damage within a living creature. Nanorobots can rebuild cells, alter DNA, accelerate neuro-response within the brain, and much more. Nanorobots have also been used to Teraform planets.
As with all Technology, nanotechnology can have negative applications as well. Nanites designed to kill targets, alter DNA adversely, damage armor, electronics, and even to destroy stars have been created and are employed.