FreeMarket is a fairly new decentralized marketplace. It is fully functional.
It runs on top of the NXT blockchain; listings are encoded into transactions and are part of the blockchain.
Many features are already released, and many more planned.
Escrow still under development (almost released)
nxtfreemarket.comThere is also a passthru service with Shapeshift integration, allowing you to purchase goods with BTC (and has a rating system). This way you don't need to run any software to browse listings, buy and sell goods.
freemarketlite.cc