Cloudscape

"The first step was covering the subject: first of all, [the nanorobots] layered themselves thickly on the surface, in the case of a person leaving only the eyes uncovered; then, they extended their outer walls; then, they connected them, so that they blocked out all light. The second step was scanning: first, they scanned the ambient light; then, they calculated where the light would go if it were unhindered; then, they transmitted the information of the ambient light to right nanorobots. The final step was invisibility: first, the outermost layers of nanorobots filled the interior of their outer walls with a special chemical; then, they caused it to luminesce with a certain hue and brightness. This hue and brightness was the same as that of the background, so that the surface could become almost invisible.

This was much like the chameleon effect, but the camouflage was perfect. The main problem with this was that this was observer-dependent: from different angles the camouflage had to look different as the background also looked different. This required a technique known as integral imaging. This allowed different images were sent in different angles, sometimes up to dozens, so that from whatever direction one looked, the subject would be invisible. Because the nanorobots were so small, this was not a problem if one had enough of them."

From Tempest II: The Novans

This is, of course, science-fiction, and therefore rather extreme: still, I believe that in reality, integral imaging might still possibly be used as a means of achieving invisibility, although perhaps not on a cloak made entirely of nanorobots.

"The exterior of the nanorobots could consist partly or entirely of compartments which could be flipped, so that either side could face either the inside or the outside of the machine. In this way, the exterior of the nanorobot could rapidly be changed to another material present in the storage of the nanorobot (if such were present): the plates of the material were deposited on one side of these compartments, which then flipped, upon which nanomagnets guided it to their appointed position. If the material was already magnetic, only one was needed, on the inside of the wall. Otherwise, the material was itself equipped with a second nanomagnet.
This process was then repeated at such extreme rapidity as is typical of such small scales, so that the nanorobots could change their exterior surprisingly quickly in this way. Other nanorobots had their exterior made entirely of these "doors," so that the process could be instantaneous."

From Tempest II: The Novans

In future, nanorobots could be used to form larger things, like cells form organs, assembling to form a greater whole. Also, however, they could be used to actually create a larger thing outside of themselves, like some cells create the inorganic matrix in bone, or like human builders creating a building. In this way, they could be used to create anything from almost any material.

Suppose that a wall of nanorobots would form in a body part (eg an arm) along the tissues; wherever they are, they imitate the function of the cells next to them; if there are no cells next to them, as in a cavity or vein, there aught not to be any nanorobots at all. In this way, every organic structure retains its normal function, even tendons, veins, and nerves. This wall then thickens, so that it becomes part of the body part, indirectly keeping the two halves together so that it still functions normally. This wall of nanorobots could then keep growing indefinitely, so that the body part would become extendable. In this way, one could, in principle, temporarily extend one's arm for meters. Admittedly, doing this safely would require advanced technology which today can only be carried out in science-fiction.

Rather than having each nanorobot obtain their own energy, nanorobots could energize one another by connecting to one another throughout whatever matrix they are in; on condition, that is, that they are present in sufficient density to form a kind of microscopic "mesh" of concatenated nanorobots. In this way, the energy could evenly be distributed and the collective system could work for a considerably longer time without renewal of energy; furthermore, renewal of energy could happen more easily, and could be done from an external electric source, because rather than having each nanorobot connect to it they could serially connect to it in a chain, like a nanoscale cable or series of branching cables.