It may be worth clarifying that these are not covers (which would be musically interesting, but not technically impressive like what we have here)

It's likely that most of these versions are not even reconstructed from the original multi-tracks : it's possible to get this result with nothing more than the original song audio + editing in Melodyne.

This is of course related to yesterday's story about Auto-Tune (https://news.ycombinator.com/item?id=15483145), of which Melodyne is a more capable competitor these days.