PrimeSense, the company behind the 3D depth sensing technology in Microsoft's Kinect accessory, has joined with two other companies to release a set of open source drivers for the device. The OpenNI project -- a joint effort between PrimeSense, robotics company Willow Garage and motion control game developer Side-Kick -- is a not-for-profit organization created to "certify and promote the compatibility and interoperability of Natural Interaction devices, applications and middleware," according to its Web site. The drivers, which also work with PrimeSense's PrimeSensor hardware, come along with a full application programming interface (API) focused on designing natural interfaces and integrating with middleware solutions. Last month, a group of hackers managed to develop and release a similar set of drivers allowing the Kinect to talk to PC and Macintosh applications. Hackers have since created everything from psychedelic art installations to simple game demos for the device. Microsoft initially reacted negatively to the release of these drivers, but soon publicly mellowed and said it supports these innovative uses for the Kinect as long as they do not compromise the hardware. The company has promised its XNA independent development environment will "eventually" support the Kinect. Through the end of November, Microsoft has sold 2.5 million Kinect units around the world.