WaveShop - Open source audio editor
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
TwistedWave - TwistedWave is one of the unique audio editors that allow you to edit your music file online without any installation.
LMMS - Make music with a free, cross-platform tool
Oceanaudio - Ocenaudio is a cross-platform, easy to use, fast and functional audio editor.
SunVox - SunVox is a small, fast and powerful modular synthesizer with pattern based sequencer (tracker).