BitThunder is by far my biggest project yet. Its a real-time operating system that uses FreeRTOS at its core. BitThunder builds on top of FreeRTOS to provide a fully featured driver model, consistent API and the usual filesystems and networking stacks required in all modern systems.
BitThunder creates a process model around the simple tasks that FreeRTOS provides, allowing all resources used by a process to be managed and tracked. This allows processes to be killed, without leaking resources. This feature requires an MPU/MMU hardware.
For more detailed information, see the main bitthunder website, bitthunder.org