Sorry if I didn't make it clear that Gumshow is in no way part of Gumroad. I also do not work for Gumroad.

I have just been trying to figure out a way to build products on top of Gumroad's great and super easy to use api: https://gumroad.com/api/authentication.

I am most definitely cheerleading for Gumroad since I think more people building markets, etc over their payments system will enable more users making money for themselves.

Update: Not everyone has a Twitter account with many followers, so marketplaces combined with other ways of getting old and new products to Gumroad could go viral.