Tomahawk is a Qt4/C++ application that implements the Playdar API: http://github.com/tomahawk-player/tomahawk
A pluggable system for providing contextual information for tracks, and artist from any Playdar source. On top of this system, two interfaces were developed:
See who amongst you friends has the worst music taste! See who's collection has got the most popular music, and who's is sorely lacking. Using information from The Echo Nest and Last.fm, this will pit head-to-head various statistics about your music library and your friends', detected on the fly from Tomahawk.
While playing a track from Tomahawk, query the tomahawk bot on Jabber for full information about the track. Ask it information from a variety of internet sources including Last.fm and The Echo Nest.