Kind of pushing the definition of RTOS here, I was expecting something like using ACE to run a concurrent program, still an interesting and informative post.
I struggled with how to convey this; the ultimate goal is to viscerally demonstrate what a thread IS, so I'm comfortable with it being... something strange... but I do want it to resemble actual concurrent systems to a useful degree.
Like, the thread scheduler code is userland code -- similar to, say, FreeRTOS -- but the "threads" themselves aren't exactly threads in an exact sense, since their context packages are entire save states for a console, not just its processor.
Also, the game code (the true userland?) has no ability to access the threading API whatsoever, which really harms the analogy.
So I went with RTOS because it's a preemptive scheduler with synchronous reschedule-on-block; where the scheduler is implemented in the same codebase as the code using it. But to be honest, nothing I know of fits.