Nanotechnology

INFECTIOUS NANOMACHINES: No. Nanomachines cannot live and reproduce inside someone's body, and they can't spread like a virus from one person to another. Any kind of infections we have are limited to bacteria and virii, and they can only do the sorts of things that are at least semi-plausible for a bacterial or viral infection. For example: A virus can mutate someone physically - that's probably not realistic, but we'll accept it as being the best fit with our established theme and background history. A virus cannot develop its own intelligence, translate languages, or cause its host to heal injuries unnaturally fast. The idea that you can have a colony of nanomachines flowing in your bloodstream, doing all these amazing things for you, just isn't going to fly anymore.

MUTATIONS: Nanomachines don't mutate recoms, but a virus can. Dr. Soliero is the expert on this subject, and anyone interested in mutagens should read her article about it. The short summary is: virus-induced mutations are highly stressful and sometimes fatal, especially if not treated. It can be possible to mutate someone intentionally in a controlled setting (i.e. hospital or laboratory) with less stress, but it's not an exact science. Nanomachine treatments can be applied as part of a treatment for viral mutations.

NANOSITE IMPLANTS: Nanotechnology would have been used to produce medical implants before the war, and these would be better in most respects than anything available 'today' in the early 23rd century. Of course, to have one of those implants, you would have to explain where it came from - considering it's been roughly 150 years since any were made.

MEDICAL NANOMACHINES: One of the few areas where new nanomachines are still manufactured and used is in the medical field. These are injected or ingested into the body, and are pre-programmed to perform some useful function: scrubbing artery walls, scavenging for toxic molecules, killing viruses, bacteria or cancer cells, inserting gene therapy, compensating for mutational stresses, or repairing some forms of tissue damage. They can be highly effective and are a powerful tool in the medical trade, but they don't perform miracles of healing massive wounds overnight or giving the patient super-powers. Neither do they stay for very long in the body. In a matter of days, or more often hours, they will run out of fuel, break down, and be cleaned out of the body, usually through the kidneys.

NANOTECH MATRIX: Also called utility fog, it's a mass of nanomachines that can rearrange themselves into different shapes. Before the Apocalypse War, artificially intelligent creatures were created uses this technology, and the most advanced ones could shape-change in a way similar to the T-1000 from the movie Terminator 2. (Some were used as "living cartoons" on television or at amusement parks!) These things have some limitations, though.... They are not physically strong. They don't eat ordinary food, instead they have to recharge or refuel from time to time with electricity or hydrogen gas, depending on the design. And they are not self-replicating or self-repairing. As time goes by (i.e. years and decades), individual nanomachines (or foglets) from the mass get lost or break down, and they can't replace themselves, so the mass of the creature is reduced. These creatures were uncommon before the war, and should be very rare today. In other words, anybody wanting to play one will be required to work with RPstaff first and justify it, including an explanation of how it survived up to present day (nanotech utility fog hasn't been manufactured for over 150 years!). The technology to create new utility fog isn't available, it was never re-developed after the war.

VIRTUAL REALITY: Instead of creating a creature from utility fog, it's possible to fill a room with the stuff and have an immersive environment similar to the "holo-deck" of Star Trek fame. Nothing in the fog chamber is real, it's all illusion created by the fog. Maintaining a fog chamber runs into the same problems of lost or broken foglets, so it's doubtful whether any are still operating today. If a small one were still working, it would be highly valuable for research. If a larger one were operating, it could become a very successful public attraction. Other forms of virtual reality are available in our setting, like the suit-and-goggles rig or CAVE displays, but they aren't nearly as effective as the "lost" technology of nanofog chambers. A nanofog chamber is the only VR technology good enough to fool someone - at least part of the time - into thinking what he sees and feels is real.

ANTI-AGING: In the last years before the Apocalypse War, a complex treatment called UAG-7 was developed that could permanently halt the aging process in humans (this is why Dr. Somtow is still alive, for one example). It was never widely available to the common people, and its secret was lost in the war. Thus, anybody wanting to play a non-aging survivor from Earth will need a special dispensation from the RPstaff. Most Furry recoms are naturally long-lived (I observed once that Furries age in "Lucy Liu years", because she's 34 years old but looks like 19.) Treatments are available to help furs age gracefully and extend their lives even further, but the medical technology to halt aging completely is no longer known.

NANO-CONSTRUCTS: Although nanomachines are tiny, many of the things built with them are large - even gigantic. During the heyday of nanotechnology, it was used to manufacture all kinds of materials and items with atomic perfection. For example: a rocket engine made from synthetic sapphire, or bi-phase carbide armor for military vehicles, or the lift cable for a space elevator. Practically anything made with nanotech would be more efficient and more effective than it's present-day counterparts (and this is why artifact hunters still occasionally brave the hazards of Earth to try and come back with something valuable).