We used state machine-based software in high assurance systems for easier analysis and synthesis. They've also been used in hardware design and synthesis. I believe LISP OS's with functional programming is similar.

All in all, many interesting and robust systems have leveraged state machine model in design. So it's really neat to see an OS that tries to build on this pattern from core up. I look forward to digging into it. Plus, might help with an idea ive been toying with about implementing an OS kernel in hardware: state machine synthesis is already good and these are state machines.