It is. Microsoft acquired it, so they probably pulled a Sparrow. :)
I would add that Acompli isn't on the AppStore anymore so it's probably a pure rebranding of the app.
Oh, I didn't even notice that. Looks like the Outlook app doesn't have the bottom buttons with links to e-mail and calendar, which would be a real bummer.
Well that explains the surprisingly fast turnaround from acquisition to release! :-)