This plugin lets you look around in-game by moving your head. To do this, it can use your webcam with FreeTrack and FaceTrackNoIR, a TrackIR camera or the Oculus Rift headset. It supports all six degrees of freedom in IVA (yaw, pitch, roll, forward/backward, up/down and strafe left/right), and two degrees of freedom in external views. Other input methods can be added in future.
For full installation instructions and links to required downloads, see the included readme, or get the latest details on the forum page.
Source included, also available on GitHub.