qtOS

qtOS is an operating system for running systems of finite-state machines. The system kernel is a task scheduler that runs processes' transitions at every cycle. Each task is activated either to be run in parallel (fork) with other active processes in the system or subordinated to the caller task, thus blocking it and creating a hierarchy of tasks. Execution of processes can be preemptive or non-preemptive and, among those with the same priority, a round-robin turn is performed.

This operating system can be used to illustrate these concepts and can also be used to suport the execution of some embedded systems.