QNX had a pretty nice embedded RTOS kernel called Neutrino, but I think they’ve been lost along the linux wayside.
Yeah. Embedded OSes are niche enough that companies have a hard time employing people just to write code that doesn't immediately meet a project need, and coders have a difficult time getting hired on just to experiment with code.
Open sourcing the OS--the bread and butter of proprietary embedded companies--solves both of these as people who just want to play around can write code to meet their curiosity, and companies can take advantage of a larger labor pool.
Models like that grow much faster than models like Neutrino where it is highly restricted.
Neutrino likely exists as it was part of a major product that a major company I worked for put out.