OpenHMD aims to provide a Free and Open Source API and drivers for immersive technology, such as head mounted displays with built in head tracking.
The only supported devices at the moment is the Oculus Rift DK1 and DK2 (rotation only).
The project is hosted on github, where the source code, downloads and usage examples are available.
Doxygen documentation can be found here.
IRC channel: #openhmd on freenode