Whoopie slings are usefull tools that allow an adjustable connection. The possible applications are virtually limitless. I can make them in multiple materials, potentially up to hundreds of feet long, to essentially any strength requirement. A whoopie can be a tiny ultralite thing to suspend a hammock or a massive tool for recovering stuck vehicles.
 
The whoopie pictured was intended to replace a purcell prussik for several jobs in rescue work. It can be attached to your harness and used as a personal teather or prussiked onto the rope to create an attachment point mid-line. 
 
I mosly put this item up to draw attention, as pretty much any whoopie sling will be an entirely custom item. I have a form to order custom whoopies for any application here: https://docs.google.com/forms/d/e/1FAIpQLSdFVWp_CfzCz4pSdgHhHheTtBPi5MbKR571ydw7RJaHziNQYg/viewform?usp=sf_link