That reports Ars Technica. It is a modified version of the popular emulation app RetroArch, containing software to play games for several old game consoles.
Microsoft does not permit distribution of such emulation apps as they are typically used to play illegally downloaded games. Previously, similar apps slipped into the Microsoft Store, after which they were quickly erased.
The creator of the Xbox version of RetroArch has released a private version in the Store, which can be downloaded via a link by anyone who is approved. Private apps do not require Microsoft to approve anything before they are distributed in this way.
In reality, there is little private about the app: the maker has now given 1,500 people permission to download it and is still working.
The Xbox app works on both Xbox One and Xbox Series consoles. On the latest hardware, the app is able to play games for GameCube, Dreamcast and PlayStation 2 smoothly for the most part.
Xbox owners have been able to install RetroArch on their consoles for some time, but then they have to buy a special developer account for around 15 euros. The console must also be switched to a special mode, which takes more than five minutes each time.
The now distributed app works in the regular Xbox environment, making it easier to use. However, Microsoft is likely to block this detour in the short term.