Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Fission - Edit audio in minutes, not hours.
Adobe Audition - Mix, edit, and create audio content in Adobe Audition CC with a comprehensive toolset that includes multitrack, waveform, and spectral display.
Audio Cleaning Lab - Looking to clean up your song recordings? Download SOUND FORGE Audio Cleaning Lab, the professional solution for cleaning & restoration with advanced ProAudio technology.
GarageBand - GarageBand is a fully equipped music creation studio for Mac
LMMS - Make music with a free, cross-platform tool