Oh, and here’s another option for iOS users that also uses OpenTrack:
The Head Tracker app is available for Free on the Apple App Store (presumably ad supported) or the full version (presumably ad free) is just $1.99:
Edit - turns out the free version of the app is time limited to 10 minutes of use to test if it works, then $1.99 through in-app purchase to unlock and use for unlimited time
Haven’t tried this one myself, but will hopefully have a look at it later today.