Calliope is an attempt to break free from imitating iTunes or Winamp. It has been a work in progress for about two years but I guess it's pretty close to a rough first release now. Code is in Bazaar, but no promises on the state of it until the project is a bit more mature.
It was started on GNOME but now runs on Windows as well using the same libraries. Decoding library is GStreamer and database library is SQLite.
New: jhbuild and msys+mingw, in which I discuss a torturous but successful week.
Key features of Calliope (some of which are entirely fantasy at this point):
Some useful links in the mean time: