VisualVox is described as 'Adjust voice recording to perfect intonation, fit it into rhythm by modifying parts, change key with minimal pitch alterations, produce perfect vibrato, visualize singing accuracy, create polyphony from single voice recording, draw frequency curves manually, and use the VST' and is an app. There are three alternatives to VisualVox for a variety of platforms, including Android, Windows, Web-based, Mac and iPhone apps. The best VisualVox alternative is Singing Tutor. It's not free, so if you're looking for a free alternative, you could try VocalBase.