From Mefi Wiki
MetaFilter Music is a site for members to upload and showcase their own songs for others to enjoy and share. Logged-in members can enjoy downloads, playlists, favorites, and podcasts of tags, playlists, and specific users.
The Music Challenges are simple: each month you can pick one idea, or incorporate more than one of the following ideas into a single composition. Be sure to tag your submissions "mefimusicchallenge" so listeners can easily follow along. Got a suggestion? Send it to [snsranch]http://www.metafilter.com/user/21223. [MeFi Music Challenge Page.]
Current Challenge Ideas
Various members have expressed the desire to collaborate. A list of available collaborators is available here.