Ruggedised versions of the PowerMAXION real time computer are now out following an alliance between developer, Concurrent Computer, and Lockheed Martin.
PowerMAXION itself is a scalable symmetric multi-processor system using the PowerPC 604e micro. Its claims to fame include real time determinism and true symmetric multi-processing on 6U VME.
You can get single board computers, multi-processors, board sets, rack-mounts, etc, and they’re all on POSIX-compliant PowerMAX OS – said to be among the most powerful real time UNIX-based operating systems. The ruggedised versions are for ultra-demanding applications, including military.