Hi @JoeA,
Could you please consider including Apache NuttX RTOS to your suggestion list?
NuttX is a very small RTOS (not so small as Mbed and FreeRTOS, starting from 16KB Flash) and it is used by many companies like Fitbit/Google, Sony, Xiaomi, Samsung (TizerRT is NuttX kernel), etc.
Thank you very much in advance!