I find this kind of thing most useful for microcontrollers and real-time embedded systems that don't require full networking. I've used many of these concepts but maybe not all at once on what many would call "bare metal" systems with no OS. Audio gizmos like cheap synths, LED nodes, things you want booting really fast with well-bounded functionality. An OS can get in the way with this kind of system if all you really need is some timers and simple I/O. You may still want a primitive scheduler, sane interrupt dispatching, and filesystems.