For industrial strength RTOS, open source is not really available. There are RT extensions to Linux, but they are still not hard real time systems. For deterministic real-time systems, there are a limited number of operating systems, and QNX (currently owned by RIM) is probably the pre-eminent one that runs on most every current processor, ranging from x86 to ARM. Take a look at www.qnx.com for more information. FWIW, I have been a QNX user/developer since 1982 and have used it to develop real-time industrial applications since then, some of which are used by the US Navy, major semiconductor manufacturers, and most of the major automotive manufactureres.