This is one part of the UCS taxonomy chart with examples of UCS's that aggregate goods that people want to offer or trade.

LEGO factory

Users can upload and share their own custom LEGO creations

• Hacking's a snap in Legoland
• LEGO Digital Designer
• MOCpages (MOC = "My Own Creation")

Prosper

Prosper is a website where individuals can lend and request to borrow money (up to $25,000).

• Prosper: the eBay of Loans? in BusinessWeek

• Q&A: 'Bringing Together George Bailey and Gordon Gekko' at WSJ.com

Trulia

Trulia is Real Estate search engine that has an active community built around it

• Trulia Voices - Real Estate Pros, buyers, and sellers ask and answer questions
• Trulia profile on CrunchBase