While working various Venture Capitol circuits, DABSquared met Alberto Savoia. In exchange for helping pretotype one of his ideas, he provided feedback to us for Curveu. The idea that he wanted to try was buying goods from and selling to your Facebook friends. People are always posting on their Facebook account when they are trying to sell an item, so the concept was to create an app that was a marketplace for that.
Had it taken off, the next steps were to integrate a whole marketplace grid showing all your friends selling activity. The version that released only posted to Facebook on your behalf using a pre-canned template.
The idea actually now exists in full as Facebook Marketplace.
I wrote DABSeller as an Objective-C (Swift was not out) iOS app with a very simple PHP back end and MySQL database. Because the app just posted to Facebook for you, all the back end did was track the post images and kept a record of your posts for future use in the app marketplace grid.