You could potentially install Android 7 on a Raspberry Pi 3 if you wanted to run that, as described by the MagPi magazine.
The binaries can be downloaded here, although I can't tell if the performance will be that great, or if it will be sufficient to run an AR application. You might just be able to use a USB camera (according to this discussion) although there's no definitive documentation as to which devices work and which don't.
There are some reports that microphones don't work all that well, and sound is known to be a problem, but it may have been fixed in the more recent versions.
If you're more interested in making the Raspberry Pi run iOS, you're out of luck—Apple are not at all keen for people to run their software on non-Apple devices.