GSnap - With GSnap you can get an auto-tune effect.
Audacity - Audacity is a free and open-source audio production software suite that includes a surprising array of editing tools and recording systems.
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.
Adobe Audition - Mix, edit, and create audio content in Adobe Audition CC with a comprehensive toolset that includes multitrack, waveform, and spectral display.
CrispyTuner - Fully featured vocal tuning suite.
GarageBand - GarageBand is a fully equipped music creation studio for Mac