There are many choices for RTOSes -- proprietary and open source. There is no one dominant RTOS because there are so many processor choices and so many different application requirements.
Here are a few popular RTOSes (proprietary)
- Integrity
- Nucleus
- RTXC Quadros
- ThreadX
- VxWorks
Here are some of the open source RTOSes/OSes
PSOS, vx works,
PSOS, vx works,