Earlier this year, Marc Weidenbaum who runs the music/art website Disquiet started a community-based group of remixers and sound manipulitists called Junto. As Marc describes it: "The Disquiet Junto is a collaborative music-making space in which restraints are used as a springboard for creativity."
An assignment is announced on Thursday evening each week and your submission has to be ready by midnight on the following Monday.
Lee Rosevere joined up and has contributed a fair number of the projects (there is no requirement to participate every week), and this page was created to collect them all, with the information about each one. All tracks can be downloaded from soundcloud, and here's more info about joining the Junto group.