GSnap - With GSnap you can get an auto-tune effect.
Celemony Melodyne - Celemony Melodyne is the perfect quick and easy tool for all your tuning needs.
Antares Auto-Tune Pro - Auto-Tune Pro by Antares is the latest and enhanced version of Auto-Tune that offers Auto Mode to correct pitch and Graph Mode for step-by-step modifications of time and pitch.
n-Track Studio - Audio recording and music creation app for iOS.
CrispyTuner - Fully featured vocal tuning suite.
MeldaProduction MAutoPitch - MAutoPitch is a full-fledged plugin by MeldaProduction that offers users precise auto pitch correction for vocals.