LMMS - Make music with a free, cross-platform tool
Celemony Melodyne - Celemony Melodyne is the perfect quick and easy tool for all your tuning needs.
GarageBand - GarageBand is a fully equipped music creation studio for Mac
GSnap - With GSnap you can get an auto-tune effect.
Ableton Live - Ableton makes Push and Live, hardware and software for music production, creation and performance. Ableton´s products are made to inspire creative music-making.
Revoice Pro - Revoice Pro is an audio plugin used for vocal tuning, time correction and ADR.