A user by the name of _miracle-max_ posted on Reddit a working release of the Drop Zone protocol, a decentralized marketplace layer written fully on top of Bitcoin. The code for this command-line only Drop Zone implementation can be found on Github.
This follows the posting of the Drop Zone whitepaper earlier this year on the cryptography mailing list by an anonymous user named "Miracle Max". It seems the author of the white paper, reddit post, and Github repository are connected, possibly the same person.
Drop Zone allows a seller to broadcast item information in a localized area and a buyer to find the listing of these items. When a buyer purchases an item through the protocol, the buyer will receive GPS coordinates of the item's location. The seller will have placed the item at the GPS location for the buyer to locate.
Drop Zone uses Bitcoin's testnet as a method to pass communication between buyers and sellers. Testnet bootstraps off of Bitcoin's network effect as all Bitcoin nodes are equipped with testnet, and sending messages through testnet is free.
Current implementations of "dark net" markets, such as the Silk Road, essentially act as a centralized e-commerce website accessed through Tor. In the past with these dark market sites, Bitcoin's utility was purely as a payment mechanism for the buying and selling of illegal goods. Sold items would still have to be distributed to buyers via traditional mailing and shipping services.
With the Drop Zone protocol, Bitcoin's utility goes beyond a payment mechanism to function as a vendor listing, messaging system, and anonymous localized supply chain built into the protocol and executed on the Blockchain.
In the author's manifesto on Drop Zone's Github page, Miracle Max writes that "I hope that Drop Zone lets us all dream of a day when no man will any longer be made to suffer indignity for simply engaging in unpopular or stigmatized commerce. May all commerce be created equal".
At the time of writing, it looks like Drop Zone's code has been forked several times. Time will tell if more development is built using this protocol.