I made a free, OpenTrack compatible head tracking app for Android - here it is running on a £90 handset, alongside a Tobii 5 and SmoothTrack
I'm working on a lot of stuff to try to make head tracking actually happen, an important part of that was making a free, OpenTrack compatible app that performed as close to dedicated hardware as possible, even on entry level devices, so that people who didn't have webcams could still have a great experience.
This clip's from the upcoming update on the Android side - someone mentioned they couldn't play on their TV from across the room so I've been working on improving the depth handling. It's getting pretty good!