This paper gives an overview of educational operating system called COLIBROS. It is small, object oriented, library operating system, based on micro-kernel concepts, supporting high level concurrency and synchronization primitives. In fact, COLIBROS is simplified operating system kernel accompanied with hardware emulation layer that emulates keyboard, monitor, disk and interrupt mechanism. A concurrent COLIBROS program behaves like stand alone program executing in emulated environment, in our case as plain GNU/Linux process. Encapsulating all critical concepts in host operating system user space makes COLIBROS development and debugging easier and more user friendly.