There are many aggregator services, which aggregate various online sources and by this media as well. This does bop.fm for online music and goes a step beyond by aggregating not just free online music services like Soundcloud or YouTube but premium subscription services like Rdio and Spotify as well.
At its About site bop.fm explains its intention. The service aims to ease sharing the music located at different services to friends, who does not have a particular account at such a service. The latter of course is a hurdle to share with friends. And even users of such various different services will be able to listen to their music more easily by not have to switch from one service to another in the case of music maybe even bought being located at these different services. At large bop.fm is an aggregator and meta service to listen to music being located at different services.
Based on the described basic service bop.fm is providing further tools like playlists. By this feature users will be able to create playlists of their tracks located at different and even premium online music sites. Furthermore the site includes features like a radio and a music search engine to find music, which reversely enable to find the sources of the tracks. To learn more visit bop.fm.