Jonathan Schmid-Burgk has released VisualVox VST, a free intonation correction VST Plugin for Windows.

With it you can:

• Shift notes of a voice recording to perfect intonation.
• Fit a voice recording into rhythm by stretching, cutting and moving parts of it.
• Fit a voice recording to another key with minimal pitch changes.
• Produce a perfect vibrato.
• Visualize how right or wrong you can sing.
• Create artificial polyphony from single voice recording.
• Design frequency curves freely with your mouse.
• Let the plugin improve intonation automatically.