Highest grossing downloadable game?

[Mephisto]

Ok guys, I need to find out what the highest grossing downloadable internet game is.

By that I mean there's a free demo that you can download from a website, and you can pay a small fee to download the full version. It's probably a small fairly simple game like a puzzle game or something made by independant developers. I've looked all over and can't find any information. Does anyone know what it is?

 

[Mephisto]

Yeah it's something like that, all I know is it's just a small game nothing like Half Life 2 or anything, probably hasn't been released in shops...etc. Was also probably developed by a small team or perhaps even one person.