Checkout has already signed up a quarter of the top 500 online retailers, largely thanks to its offer of free payments processing until 2008.

ECONOMIST: Online payments

Along with the explosion in mobile technology to support commerce, startups like LevelUp have begun disrupting the payments market by offering free payment processing in return for paid loyalty and marketing services, showing that we are quickly moving into an age where the value of payment data exceeds the value of transaction fees.

FORBES: Mobile Payments: The Case For Choosing An Open Platform

Csound is a free language for sound synthesis and processing.

ENGADGET: How-To Control Csound with a Custom Midi Controller: Introduction (1 of 2)