Microsoft has released the Xbox One SmartGlass app on iOS and Google Play devices.
I had a little play around with it last night on the iPad, although it's a little limited at the moment for me since I've yet to receive an Xbox One. Still, at least I managed to sign in and have a look at friends activities, as well as being able to check out some gameplay clips which have already been uploaded for games such as Ryse.
You can download SmartGlass for iOS here.
The Android version is here.
Let us know what you think once you have some time with it.