Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
LMMS - Make music with a free, cross-platform tool
GarageBand - GarageBand is a fully equipped music creation studio for Mac
Oceanaudio - Ocenaudio is a cross-platform, easy to use, fast and functional audio editor.
Adobe Audition - Mix, edit, and create audio content in Adobe Audition CC with a comprehensive toolset that includes multitrack, waveform, and spectral display.
Ardour - Record, edit, and mix on Linux, Mac OS X, and Windows.