That’s the thing, hard to have experience with multiples. People generally stick to learning one or two. I know RTX and FreeRTOS differences, but I know without a doubt I’ll try NuttX.

I starting looking at RTOSes when you were lucky to have 3 or 4 options anywhere - and it wasn’t that long ago!

Now... with Amazon owning FreeRTOS... Intel and Nordic and Others going heavy in zephyr for multicore... professional but niche options like RTX, Segger’s OS, and a hundred others... and if you chip has a MPU/MMU someone is trying to get Linux on it (whether it makes sense or not!)...

I think the market is getting pretty crowded. Personally the viable options right now unless you need something large like VxWorks for Java runtime, I think it’s a choice between Amazon FreeRTOS and Zephyr.