Many games and simulators nowadays support headtracking. That means, that a tracker determines the pose of your head (rotations and translations, or 6DOF). The headpose is then 'amplified' and filtered by a program (for instance FaceTrackNoIR), so a relatively small movement of your head is translated to a larger movement 'in-game'. The program sends the manipulated headpose to the game, which shows this movement, by manipulating the 'camera'. Many gamers already use a headtracker, most of the times one using a webcam.

FacePoseApp is an App that turns your smartphone into a smart face-tracker. It has some big advantages over face-tracking with a webcam: the user does not need to buy a webcam AND the PC running the game does not have to spend valuable CPU/GPU-power to track a face. FacePoseApp sends the 6DOF to the external program over wifi (this feature can be unlocked, by upgrading the App). 

The App only features a very small number of buttons and settings. For more information about these you can visit the faceposeapp website.