This is something I'm playing around in Hedgerow Hall... having the entire game economy revolve around player skill interaction.
For instance, instead of having a weapons shop, there's a place where you can forge weapons instead, if you have the right skill. However, forging weapons requires ore, which takes a different combination of attribute/skill than does the act of forging, so it's not likely that anyone's going to be really good at both.
It works like this: Shrews are expert scroungers, so they're like the primary producers. A Shrew goes off into the woods, collects an armful of pebbles, some strips of bark, some assorted leaves, some bits of iron, some assorted berries and nuts, some little quartz crystals, and so on. The Shrew can eat the berries, fling the pebbles at enemies, and put the nuts to either use, but other that, the rest is just junk to the average Shrew. A scholarly Mouse might be able to put the crystals to use in some wizardly pursuit, or make use of the leaves which have medicinal value. A big burly Badger may be able to turn the iron into weapons. A nimble and clever Squirrel might be able to fashion the leaves into a sort of blanket, make a cup or bowl with the strips of bark... or use the bark to make paper and a leaf to make a pen.
Now, here's the thing: this game has no currency system. What prevails upon Shrews to part with their hard-scrounged "treasures?" There's the fact that the Shrew can't do anything with most of the stuff they'll turn up... they can just dump it on the ground for anyone to take. Still, if the crystals you find are going to end up in the paws of a Mousey mage anyway, it's better if you can get credit for it... a wizard friend can be a good friend. And obviously, if someone is practicing medicine, it's in all friendy creatures' best interest to make sure that they have a good stock of healing herbs. So, sharing goods helps form social ties.
Then there's more direct interaction... it doesn't take much iron to make a weapon fit for a small rodent, so a Shrew with a lot of iron can prevail upon a Badger to make a small sword or a lot of throwing blades and let the Badger keep the rest of the iron. Players can also split the fruits of their labors... making berry wine (which concentrates the revitalizing powers of the various berries) requires three things: berries, the brewing skill, and a vessel to hold the end product. That's three different skills. Three characters could work together for a while to make a large quantity of wine, and then each take 1/3rd from the final "profit".
Of course, the system works on trust: the Badger smith you take your ore to might just accept the ore, make its own weapon, and flatten you with it. It might not even be a smith. It might not even really be a Badger (wily foxes!) A Shrew who's been out in the woods, heading back to the hall to barter, might be waylaid by bandits, or might be set upon by thieves while sleeping between scrounges. This is another area where social ties become important... having an ally out with you to watch your back while you sleep, or recover stolen goods and take revenge.
The main problem with this system is inflation. Once everyone has an appropriate weapon, for instance, iron ore is just junk, to be left lying around or given to new characters for nothing. Berries and their byproducts get consumed, but the wooden dishes that hold liquids get left behind. Good from the point of view that a veterarn brewer is going to be able maintain a larger stock than a novice one, but when people start getting more bowls than they can carry or manage, they're going to start leaving them around, too.
A possible way around this are to make every item "disposable": blankets can tear, pens can break, swords can be shattered, any item will degrade/disappear if left unattended too long.
What does everyone think about this system? I think it, along with liberally enforced roleplaying guidelines, will help encourage character interaction in a world nearly devoid of NPCs (and I may get rid of the ones that are there... make it so you choose your skills at the beginning, and if you want to learn a skill you don't already possess, you must have someone else teach it to you.)
Groups of characters who have good experiences with each other and can trust each other will naturally form an organization without any sort of hardcoded "clan" system... there may also be a general pool of reputable craftsanimals that new characters can turn to. A group of allies might set a goal, like creating a stockpile of restorative wines for themselves, or creating a magical weapon of legendary proportions, that could occupy them for weeks and attract the attentions of envious groups.