A friend of mine just got a job at Swapdom, which organizes multi-way swaps of clothes among people who don’t want them anymore and want to rejuvenate their wardrobes. You can search the community and point to things you would like and things you’d happily give up in exchange for them, and they find swaps that actually work. In particular they orchestrate multi-way swaps (A gives to B, which gives to C, which gives to A, or even longer cycles).
If you’re Alvin Roth, you can win a Nobel* Prize for this stuff. At least if it’s kidneys being traded instead of clothes. The Nobel foundation has both popular and technical expositions of his work in market design; the largest kidney swap in history, a few months ago, involved 28 kidneys.
(Disclaimer: I don’t actually know what’s going on behind the scenes with Swapdom’s algorithm; my friend is not a technical person.)