KGuitar is powerful KDE-based music tabulature editor with support of guitar, drums, classic note scores, MIDI synthesizer output, chord, scales, modes, melody and rhythm construction and analysis tools, lots of tab effects, Guitar Pro files import.
eXtace is a 3D audio visualization tool (or eye candy depending on how you look at it). eXtace requires ESD (Esound) for its sound input source. It performs a FFT (fast fourier transform) on audio and displays it via various graphical modes.