Jokosher - Jokosher is a simple and powerful multi-track studio.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
SoX - Sound eXchange is a command line utility that can convert various formats of computer audio files...
Spek - Spek helps to analyse your audio files by showing their spectrogram.
DSP-Quattro - DSP-Quattro
Fission - Edit audio in minutes, not hours.