My guess is that it is a RTOS of some kind. There are numerous commercial RTOS's out there that run on embedded microcontrollers - no sense reinventing the wheel. I have used a few RTOS's in microcontroller apps and it makes writing your firmware darn near as simple as writing a threaded app for a regular OS. It's amazing how little memory some of these RTOS's take when your used to a regular OS. There are several that are less than 10kb in size