Essentially, Gumroad allows users to sell Online (& even Offline) using shortlinks but the way it does this is what makes it unique. Users can send a payment mechanism built inside the link they are about to share with others Online, thus turning the whole exercise into a sales tool without any of the accompanying headaches like a separate payments tool like Paypal...& so on & so forth.
So you can use Gumroad to sell all sorts of things on the Internet. That song that you recorded but never turned into an album, a short story, maybe your study notes...virtually anything (pun not intended). I repeat - to sell you do not need to set up or have any payment platforms like credit or debit card payment systems set up. Gumroad takes care of that, of course for a small commission (5% of each transaction)
The other thing about Gumroad is that it was founded & is run by a whole lot of teenagers, some barely in their 16s.
Compared to the last few months, in June 2012, the race between Startups for the title of 'The Most Useful....' was tight. The runners-up in June were:
a) Iris, which is the Android version of iPhone's Siri
b) Carat, a Smartphone battery saving App
c) Fliptop, a Social Intelligence gathering platform
To read up with the write-up on Gumroad, you may go to http://www.whatsnewonthenet.com/