UOS-LPC800 is a real-time operating system for NXP LPC800 series.
It provides multi-tasking, sleep, yield, and message-passing features in your design easily.
You can select the scheduling algorithm such as Round-Robin or Priority-Based.
Please see uosdef.h for the details.
The implementation of the kernel is really simple.
You can learn how the RTOS works, and how RTOS implemented by examining the source codes.