We're a platform for long tail merchants. So for example - you'd sell the psd your not going to use in your app on gumroad, but you'd sell the final app through chec. - if that helps. - we also only charge 3.5% and can do a lot more with downloads + handle physical products.
We position ourselves between Gumroad & Shopify (if they did payments).
on a side note - me and sahil know each other well. Back in april 2011 when Chec was called Kout I actually reached out to him to join Kout after he launch groad on hackernews. He said "you've already built the software why do you need me" but we've kept in touch and occasionally get coffee and discuss the space.
Link based selling has been around for years. 2checkout, 1shoppingcart, paypal, ejunkie, quixly etc have been at it for a while. I came up with the idea for Chec after i ended up throwing a PayPal checkout in an iframe for a info product i was selling.
P.S - if anybody is wondering about the 2 year gap between launching - that story will come to light shortly.