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=master

This 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.