Five is a streaming media framework designed to efficiently expose media hosted on your home PC via your cell phone's data connection. It does this by passively synchronizing meta data and actively streaming/caching the media itself.
Currently only music is supported, with a rich player included, however this concept is planned to be expanded to photo albums, stored videos, etc. Likewise, a proof-of-concept desktop version is in the works.
Check out the project page hosted with full source code at Google Code: http://five.googlecode.com/