Monofilament bolas. Three weighted balls, a monofilament line running from each to a center tie point, grab one of the balls and swing it about, then release it in the direction of your target. A little risky if you're not skilled with the things, keep an ice bucket handy in case you need to get a finger reattached, but nasty - the target is not going to just disentangle himself and walk off.
I'm going to respectfully disagree on the points about weapon penetration. Obsidian makes for one wicked arrowhead, sharper than surgical scalpels - we just prefer steel because obsidian's very likely to break in use. If a weapon point or edge is sharper - i.e. the impact energy is being applied initially along a much smaller cross-sectional area at the microscopic level - it will defeat the resisting material much easier, penetrating more easily for the same amount of energy. If the remainder of the weapon has reduced friction, it will spend less energy penetrating the same amount of matter - in other words, it will penetrate deeper for the same amount of energy. Yes, an edge that fine is more susceptible to damage, but we're envisioning science-future specialty materials: if we can imagine monofilaments, we can certainly imagine obsidian-fine edges of superior durability.
What that amounts to in game terms, I don't know. I wouldn't go overboard, but I would definitely give it a small bonus to penetration and damage, perhaps a +1 over the traditional item. Nothing overpowering, but players do appreciate having those little "edges".
Other thoughts come to mind. A cane with a superdense metal head would carry more of a wallop than the typical cane, possibly enough to surprise your opponent and cause him to rethink the idea of mugging you - and should be perfectly legal on those no-weapons high law worlds. A hypertech uber-sharp knife that kept its edge might only be given a slight damage bonus, but it's one very useful tool for other needs - definitely the way to go for bayonets for an elite force that might have to rough it in the wild.
It might also be possible to use high-tech materials to make swords or knives with surface micropores that can hold tiny quantities of some chemical agent - say an irritant that would make the wound very painful, causing the injured party to be more likely to withdraw from the fight, or at least to be a lot more distracted - to bend the words of the great Ali just a bit, "float like a butterfly, sting like a fire ant"; the sheath would be a part of that tech. Imagine the reaction of your opponents when one of their number fell back screaming repeatedly in surprise and agony as his wound flared with a sensation like someone holding a blowtorch to his skin. People tend to fear pain worse than death.
Or, a foil that delivered an electric charge like a stun-gun, stunning your opponent for a few vital seconds, possibly enough time for a quick and more lethal second thrust - and imagine the surprise if your opponent tried to parry or grab a weapon like that.
Other ideas involve taking advantage of stronger or improved materials for hinges, locks, and springs: a staff with a springblade spearhead, a hand-axe with a T-shaped axehead with hinges at the intersection of the T and at the handle can fold its blade away in the handle for easy storage in your survival backpack, a broadsword with a blade that disassembles into three or four parts for easy storage (I recall a gimmick like that from Highlander).
