Spectrum3d is a software for Linux that displays the harmonics of the sound in 3D, either in real-time or from a preloaded file. It is optionally multitouch and compatible with JACK.
It uses OpenGL, SDL (or GTKGLEXT instead), Gstreamer, Gtk+ and (optionally) libjack and uTouch-Geis.
amazing, very useful, and critical for certain aspects of audio processing
Thought you might like to that I reviewed Spectrum3D for the Linux Journal: http://www.linuxjournal.com/content/short-notices-news-linux-audio I hope you like the review. Your software is excellent.