This is one area in which the main CP 2020 rules seems silent. But if the applications for nanotech are impressive in the world of medicine their effect in the realm of death can be just as great. This section is not intended to be definitive, but is hopefully a start point from which your own imaginations can leap.
Osteoperosis in a can. Just imagine being able to afflict a foe with near crippling bone weakness. A nasty situation to be sure. This brand of nanomachine has a very simply life span and program. Designed to pass through the skin the nanomachines make their way to the bones where they begin to remove calcium from the bones, rendering the bones brittle and weak. All impacts that do damage, and nearly 50% of sudden movements can cause bones to break. The nanites have a very short life span, only a matter of days. Once they have run their cycle the patient begins to recover, and each week of normal health will reduce the break risk by 10%. (This is for game ease, in reality the restrengthening of the bones would probably take months and months of high calcium diets. There are nanotech cures that will reverse the condition in just as short a time frame.)
This nanomachine not only kills, but is very effective. The only side effect, a long painful death. But then sometimes that's what the boss ordered. This nanite kills by attacking the blood and the bone marrow where blood is produced. The nanite damages or destroys the body's blood or blood production capability. Eventually the patient begins to bleed out from any part of the body with a route past the skin, such as: tears of blood and blood sweat, out of the ears and through the excretory systems. Many internal organs such as the eyes and lungs can fill with blood. The patient suffers 1d4 damage each day until death. The only known cure is nanotech based.
This nanite is designed to play particularly nasty games with a target's DNA (Deoxyribonucleic Acid: The primary medium for the storage of genetic information.). It is able to target a specific cell type, and once there find its way into the nucleus. The nanite is built to activate the various oncogenes (Oncogenes: A normally dormant region of DNA thought to be responsible for the onset of various cancers when activated.) in the target's DNA. The result is a lethal cancer that is inoperable under the normal procedures. The patient has up to 6 months prior to death. Again there is a nanotech cure, one that can be applied to perfectly natural cancers.
On the streets of any modern city the police often have to deal with well armed and well armored criminals. To make matters worse the cops are not always free to use the appropriate level of response. But with the modern criminal it often comes down to kill or be killed. One way to correct this stalemate is to remove the criminal's armor. But up until now acid has been the only viable solution to kevlar's universal availability. But acid has its own side effects. The vicious acid burns have often proved enough for lawyers to free their clients, even in 2020 police brutality catches people's attention. So the police arranged with Militech to create a new brand of basic nanite, one that finds kevlar irresistible. The new anti-kevlar nanite is delivered in a paintball round, or in a liquid medium. It is capable of stripping kevlar armor of 5 SP's per round, for up to 3 rounds. It has absolutely no side effects when exposed to human tissue.
Nanotech can be so dangerous that people rightly fear it. As a result the most people that have even a clue about its lethal applications are more than willing to run to the nearest hospital as soon as nasty unexplained things begin happening to their bodies. Most hospitals are equipped to inject neutralizing nanites, or begin the research needed to find a new agent. Therefore occasionally a new breed of killer nanite is introduced. This is such a monster. It works on mammals in much the same way that the insecticide DDT (a chlorinated hydrocarbons compound awarded a Nobel Prize in 1948, banned from all but emergency use) does, by affecting the transmission of nerve impulses. DDT killed literally by burning out an insect's nervous system. The nanite based variant works under the same principal, but is designed to function slowly. The target begins to receive a +1 bonus to all initiative and reflex checks each week till death occurs on week 5. The effect is so gradual and beneficial that most infected targets will never think to get medical attention.
This is the latest word in knife design. Before activation the weapon resembles a large knife hilt. Inside the blade is a supply of specially modified metallic alloy and a set of rechargeable nanites. The blade is equipped with a set of options, generally several different knife designs for different functions. Upon activation the nanites begin to weave the liquid metal into a rigid and very effective knife blade. The effect is oddly organic and may take a few minutes. Obviously this is not a fast weapon, but it is very adaptable and when deactivated can be hard to spot. The weapon concept can also be found in limited use models, a small supply if the liquid is provided with a one form one use nanite, the ultimate in hard to spot weapons. A liquid can be stored in a wide variety of containers and doesn't show up as metal on X-ray or metal detector, not until the nanites go back to work and rebuild the metal on the molecular level.
The other uses for this material should be obvious. A much more expensive model could allow thieves to custom create any key they need. Imagine a load of bullets that could be altered to reflect the needs of the current shoot. AP rounds can be altered into soft impact mushroom rounds for massive tissue damage, or maintain a liquid center for hydrostatic shock damage.
There are of course draw backs. The speed factor for one, don't even consider trying to pull this weapon by surprise without preparing it first. Second the implement or blade always resembles a high quality mirror for reflection. Next if the blade snaps that part of the special metal is lost, the nanites removed and deactivated. Finally if power is lost the blade is useless.