Not really an RTOS. I hear it's more an "event loop and some interrupt handlers," much like the firmware in the Kinect.
(We went through a "we need an RTOS" phase on the Kinect. Eventually we ditched the thread stuff we wrote, which made things a lot simpler -- if you don't absolutely have to have threads and can get away with computing stuff in a main loop, then do that. Threads introduce all kinds of synchronization and inconsistent execution time nonsense that you should avoid if you can).
(We went through a "we need an RTOS" phase on the Kinect. Eventually we ditched the thread stuff we wrote, which made things a lot simpler -- if you don't absolutely have to have threads and can get away with computing stuff in a main loop, then do that. Threads introduce all kinds of synchronization and inconsistent execution time nonsense that you should avoid if you can).