This semester Thomas Czernik and I work together with three MultiMediaArt students (Marta Todorova, Benjamin Hinteregger and Wolfgang Schütz) on a music player like semsix for Facebook. That is Facebook users will be allowed to search music on Youtube and to organize it in playlists via our application. The difference between our music player and semsix or other similar implementations is the social part of our app. Facebook enables our users to share their playlists by posting them to their walls or by letting them work together on collaborative playlists with their friends. At the same time, the user interface is designed to be lightweight and easy to use. So our player will not be overloaded with features, it will be easy and effective! 
We already started implementing the player using the Flex 4 framework for Flash and we will be finished on January the 15th 2009. For storing the data needed by our app (Playlists and their tracks for example) we use Ruby on Rails in combination with RubyAMF to easily exchange data between our Server and our music player using the AMF data format.
Here is a picture of status quo. I prefer to mention that this is not the final design, in fact it isn’t designed at all 
Studying MultimediaTechnology in Salzburg, Austria 
Looking forward to the final app.