Why?
Linux covers that kind of hardware so much better already.
Because it would simply be nice to see something different once in a while. Don't get me wrong, I like Linux... I'm just a bit bored with it.
Agreed. I ended up settling on RTEMS, which isn't an RTOS, exactly, but it might as well be.
RTEMS certainly is a real time operating system. It was initially used in missiles and the original meaning is Real Time Executive for Missile Systems. Later adopted for generic military, scientific and space use.
I think it is a great open source RTOS. FreeRTOS and Contiki are good but not really comparable. Their focus is on smaller more memory constrained systems.