It was a surprise to everyone when somehow the Win64e10 N64 emulator managed to end up on the Xbox Store. It wasn't officially listed, since it was still going through approval, but for those who knew to look for it, downloading the emulator was a cinch and before long they were playing all manner of N64 games on their Xbox.
Now though Microsoft has stepped in and removed the product from the store. However in a gesture of goodwill, it's not going to strip the app from people's accounts, so if you managed to get in there quickly and download the emulator you'll be able to hang on to it.
Unlike most emulators though, this one did actually require you to pay for it. It went up priced at $10, partially because it needs a price to get onto the store, but also because it utilises a slightly different system than your average emulator.
To get it to work, you have to download the games and store them on your OneDrive storage account. From there the emulator can grab the ROM files, making it possible to play the game. It will then upload a save game when you are finished playing, so that you can continue later where you left off.