So, from the following link (Difference between OpenNi and NITE), I understand what OpenKinect and NITE are. What is SensorKinect and how does it fit in the picture? From my current understanding, we don't need it.
In case anyone is wondering, I'm intending to use these libraries for skeleton + depth tracking.
SensorKinect is an OpenNI module that allows it to talk with the Kinect. Basically, OpenNI and NITE are middleware and SensorKinect is the hardware driver.
If you're using a Kinect, you need it. If you are using a PrimeSense sensor, you don't.