The operating system universe is a lot bigger than most people have been led to believe. They think it's windows vs linux vs osx. If you're 'wild' you go *BSD.

The operating system universe is a lot bigger than most people have been led to believe. They think it's windows vs linux vs osx. If you're 'wild' you go *BSD. There's a lot more out there - unikernels in particular are similar in nature to RTOS (like the system that is on the Mars Rover) and they definitely descend from the microkernel branch of the tree. Having said that many microkernels tend to be multi-process. There are now over 10 different unikernel implementations out there currently. They all have different aims and goals but I'd say one defining characteristic amongst all of them is that they are single process by design. There's many other considerations but that's the most important one that comes to my mind.