Nanotechnology is the technology of developing microscopic devices. The best known variant is nanorobotics, the creation of microscopic robots, which are generally expected to be used in medical applications and computer manufacturing. There are also many other potential uses for nanotechnology including make humanity healthier and improved (disease resistant, faster, stronger, better sight, etc..).
Military orgsanisations will of course be interested in tiny, microscopic killing machines among other applications. How concerned should we be? 
- ↑ How Nanotechnology Works
- ↑ What is Nanotechnology? This has a cool video of a geer where individual atoms or molecules show.
- ↑ Military nanotechnology - how worried should we be?