Nanotechnology, if developed to its fullest potential, has tremendous revolutionary applications.  In medicine, nano size machines can be injected into a patient with cancer.  The machines would then target and neutralize the cancerous cells. Nanomachines can also be used to manufacture products.  In fact, nanotech visionaries have predicted a future where nanotechnology could shift the means of production from macro size, smoke stack facilities to counter and desk tops in our homes and work places.

Imagine a device called a personal nano-factory that can produce basic to complex items from the ground up, meaning molecular/atomic assembly.  Star Trek's replicator comes to mind when envisioning finger tip manufacturing.

Other nanotech applications include using nanomachines to cleanse the air of pollutants, water treatment, and computer data storage.  There is of course the other side of the coin.  As atomic research brought forth the atomic bomb, nanotechnology could give birth to a host of terrifying weapons.  

As matter can be assembled at the molecular/atomic level, so it can be disassembled.  Science fiction has and is exploring both the positive and negative uses of this very intriguing and new avenue of human knowledge.