This is a simple spotify client. When starting up you login and chose a playlist, which it then plays while visualizing it. The effect itself is based on an FFT and a moving average. To be honest it doesn't follow the music quite as well as I wanted it to. Despite that it seems to work well enough.

You'll have to download libspotify to compile it. You also need your own API-key which should be placed in a file called appkey.cpp.