There is however also TRON:

https://ethw.org/Milestones:TRON_Real-time_Operating_System_...

which was demoed running on an 80186 with _multiple_ windows running videos w/o dropping a frame.

Described as "The most installed operating system in the world":

https://www.linuxinsider.com/story/the-most-popular-operatin...

Unfortunately, the U.S. State Department viewed the Japanese plan to place it on all computers in their educational system as anti-competitive.

Really wish it was available for the Raspberry Pi.