Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
WaveShop - Open source audio editor
LMMS - Make music with a free, cross-platform tool
TwistedWave - TwistedWave is one of the unique audio editors that allow you to edit your music file online without any installation.
Oceanaudio - Ocenaudio is a cross-platform, easy to use, fast and functional audio editor.
Ardour - Record, edit, and mix on Linux, Mac OS X, and Windows.