Mark3 RTOS
Open-source RTOS and Embedded Systems Toolkit for C++ and C
...The carefully designed object model drastically reduces the overall size and complexity of the source code, leading to enhanced code reuse, stability, and modularity. It also makes the source easier to understand - any experienced C/C++ developer should be able to understand the relationship between objects in the system, as well as use and extend them to fit a given application.