I need a few C/C++ components to implement the Plain VM, one of them is a RTOS . I wrote my own RTOS that runs on both Arduino, ESP32, STM32, Windows and Linux years ago. It is a simple linear scheduler. I found it quite handy even on Windows applications as it scale better and have some good timing/signalling schemes.
The principle is simple as we loop executing task after task, but controlled by timing parameters and signals. This means we execute a single instruction in each VM before we continue to the next VM.
We will be using this stand-alone as well as together with FreeRTOS, Windows and Linux.