1. A robot of microscopic proportions, presumably built by means of nanotechnology. As yet, only used informally (and speculatively!). Also called a "nanoagent".
2. Tiny autonomous robot.

Nanomachines are largely in the research-and-development phase, but some primitive devices have been tested.

An example is a sensor having a switch approximately 1.5 nanometers across, capable of counting specific molecules in a chemical sample.

The first useful applications of nanomachines will likely be in medical technology, where they could be used to identify pathogens and toxins from samples of body fluid and destroy them.

Another potential application is the detection of toxic chemicals, and the measurement of their concentrations, in the environment.