There's no vaporware which allows for a decentralized exchange yet. This dev programmed it himself.
The code that implements the Sling marketplace is unique (not copied from another alt-coin) and implemented in this C++ class:
https://bitbucket.org/dgslayer/sling/src/0c2671e70fabc62d6b64ca8d900af4e23b0bf57b/src/market.cpp?at=masterThis is a rough, rough draft of Sling HTML5 facelift version I am working on:

I ported Shadowcoin code to makes these changes. I am going to complete the HTML5 and finish wiring it up to the original Sling C++ code using a bridge class.
This is very encouraging to see members of the community getting active on this project.
Handshakes of acknowledgement all round

It can get very lonely but this spurs me on.