Continuing the trend of having anything good requiring building it from scratch, much like the 8 bit days, lions have pondered a new phone app which shows the magnetic heading over the camera view in varying zoom levels.  The user could screenshot it but not be able to do anything else.  It would have a reticule on the heading.  It would reorient for portrait & landscape mode.  It would only show a lowpass filtered number for the current heading.  It could possibly show a heading corrected for magnetic declination, looking it up using curl.  

There's nothing else but poorly written adware for doing it now.

A practical use for it is hard to come by.  It's kind of a survival tool because finding accurate bearings is something animals do in war.