PrimeSense, the company behind Kinect has released open-source drivers and established an Natural Interaction devices, applications and middleware organisation named OpenNI.
According to the official site :
The OpenNI organization is an industry-led, not-for-profit organization formed to certify and promote the compatibility and interoperability of Natural Interaction (NI) devices, applications and middleware.
As a first step towards this goal, the organization has made available an open source framework — the OpenNI framework — which provides an application programming interface (API) for writing applications utilizing natural interaction. This API covers communication with both low level devices (e.g. vision and audio sensors), as well as high-level middleware solutions (e.g. for visual tracking using computer vision).
Here is a video showing off real-time skeleton tracking.
More info and downloads at the Official Site.