I've been developing an Amarok-like clone for the Windows platform over the past few months as part of a college project. Recently as the deadline nears I've been going on more and more bughunts and the applications now become usable by myself as a proper player.
The codebase is still very simplistic in comparison to the likes of Amarok and iTunes obviously, but it has a central playlist with drag and drop reordering as well as lyrics fetching support and a tree based display of the collection. While I'll probably make a major overhaul of the database backend and structure for now the single table approach will have to do.