A Beta Xbox Live Extras showed up in the Windows Phone Marketplace on June 10 just to be quickly removed later as it turns out that the application was intended for those users who are already testing out Mango update of Windows Phone.
You won’t be able to find it anymore but the details of the application were: date added 6/9/2011 and version 188.8.131.52. It was most probably never intended for public sighting nor usage as it is probably a beta destined for Mango users (testers). Even if you somehow managed to grab it you won’t be able to run it as it depends on certain files and libraries your NoDo doesn’t have (but Mango does). The app has been removed and replaced with the 1.6 version everyone can grab.