There are several ARM Cortex M4 compatible RTOS available in the market, however at this time Hilscher has limited experience with these and we do not have a RTOS example available for netX90.
Hilscher provides the CIFX-API and CIFX-Toolkit for developing the necessary drivers for your chosen RTOS. More information on the CIFX-API and CIFX-Toolkit can be located here: https://kb.hilscher.com/pages/viewpage.action?pageId=73208724