David,
They are apparently relatively new. Built for retailers, to help the retailers market on social media.
Nearest I can tell they are a socially-media-driven fulfillment service. A retailer runs a promo. But instead of dealing with the retailer, you register with shopsocially giving them all your personal information, credit card, and social media info. You buy a voucher from shopsocially and pay the retailer for the promo with it. In the process, everything is social-media-broadcast. You can also earn points, etc. by social-mediaing the retailer who ran the promo.
They seem to be extremely popular with the "social-media-driven giggling 12-year old girl who will give her personal information to anybody and everybody who asks" crowd which was enough for me to stay far away.
As said above, I have written the retailer (canvas printer in this case) to ask if all future promos will be driven thru shopsocially. They have not replied.