Nanoprobes are an advanced form of nanotechnology that appear in the Star Trek universe. The Borg use these microscopic robots to assimilate new technology and new lifeforms into their collective, becoming more powerful with each new acquisition.
Borg drones carry out assimilation by injecting nanoprobes into their victims using the tubules installed in their arms. In living beings, the nanoprobes rewrite the DNA of their victim and cluster together to form various cybernetic implants that enhance the functions of the victim's body. In technology, they hijack the functions of the machinery they infect and reconstruct it to suit the Borg's purposes. Nanoprobes are the foundation behind all Borg technology and are present in all their systems. Whether they developed nanotechnology themselves or acquired it somehow remains a mystery.