FreeRTOS.orgTM is a portable, open source, mini Real Time Kernel written by Richard Barry - a free to download and royalty free RTOS that can be used in commercial applications. More general information about FreeRTOS can be found at www.freertos.org
An experimental adaptation of FreeRTOS that runs on NIOS II is available for download from www.ixo.de/info/frtos_nios2
From V5.4.2, FreeRTOS contains an official Nios II port and demo application. See http://www.freertos.org/FreeRTOS-Nios2.html for more information.