OpenNI it's one new organization to promote the compatibility and interoperability of Natural Interaction (NI) devices, middleware and applications PR Newswire.
OpenNI can be use with Windows and Linux , both 32 and 64.About OSX , the OpenNI SDK will coming soon.
What is OpenNI SDK?
The OpenNI framework is an open source SDK used for the development of 3D sensing middleware libraries and applications.
Read more about OpenNI : here.