The ABBA world has been in a bit of a frenzy of late with some previously unheard mixes doing the rounds.
The conjecture being that they are work in progress reference mixes, created especially during the development of the Mamma Mia! stage production from over a decade ago.
Whatever the truth, they are mightily impressive and moreover very much welcomed; as unlike the plethora of rare audio we see released by Elvis on a regular basis; unreleased and/or alternate ABBA material is very thin on the ground.
Enjoy them. I don't think they'll be on YouTube for long!
(N.B. All of these links are private uploads only - with more to follow soon.)