Been really busy trying to finish my game up but I had a chance to install and test this OS last night :
Real-Time Executive Manager
The Vault-OS source code is currently targeting FreeDOS, Win32 and Linux systems but this OS fully supports POSIX and BSD standards which are the only requirement to compile VOS source.
Neat to think about Vault-OS running on the same OS as satellites and military hardware. Compiles to ARM targets as well which is a very cheap 32 bit board at the moment.