Hello Richard In FreeRTOS Features overview section, it is mentioned that FreeRTOS.org is a scalable real time kernel designed specifically for small embedded systems. The word small in above sentence triggers the following question: Do we have any known constraints if we use it for big & complex embedded system projects? Is my understanding correct? Regards

FreeRTOS is designed to be used in small to medium sized microcontrollers – but these terms are relative.  If it is suitable for your application, then there is nothing to stop it being used in any embedded system of any size.  I suppose the caveat to that is it does not have MMU support, so there will be a natural ceiling to its usefulness if you need an MMU. Regards.