I'm not sure what you'd call it, but imagine a website where if a normal Joe had a widget they wanted to sell, they could sell it directly to another person and the market would take a small cut.

ebay? lol

Tangible

Like a classifieds type site?

Going to hard to compete with craigslist in the US.

yeah, ebay and craigslist are the 1M lb gorillas... great reason not to go this direction... I was thinking about a very specific use case.  Again, just playing around with ideas. Doubt I'd go this way but if there was readily available software, I'd check it out.

There are some classifieds packages, but it's been a couple years (probably more) since I looked and don't know if they're matured or forgotten or what by now.

I stumbled across open-classifieds.com recently. Don't know a great deal about it, but it looked quite useful and more polished than some of the alternatives.