You can try ucos. It's fully documented and free to get souce code that it has been transplant on nxp's soc.
Hi Eng.suhail,
You have several options.
MDK-ARM includes RTX RTOS example projects for a LPC2130 board (the MCB2130).
I also got a few hits when searching for FreeRTOS and LPC2138.
Hope this helps,Johannes