[rzr]

NuttX worth considering if you're coming from Linux background, I liked it and related community, BTW they have a workshop later this year.

Back to the subject implementing drivers can be a good warmup exercise, you can get inspiration from hints I have shared:

https://rzr.github.io/rzr-presentations/docs/nuttx/

[fellerts]

How does it compare to e.g. Zephyr or other RTOSes?

[acassis]

I think the best way to compare is trying NuttX and others RTOSes on some supported board (raspberry pi pico, esp32-devkit, stm32f4discovery etc). As rzr said NuttX is easier for people with Linux background, because it is Linux-like. So the way you mount a MMC/SDCard is the same, the way you search for devices using i2ctool is the same, etc.