GeekOS
The goal of GeekOS is to be a small and realistic OS kernel.
Earlier versions of GeekOS have been used as the basis for student projects in operating system courses. This new development version of GeekOS is a rewrite designed to address limitations in the original version. It is not specifically designed for course projects, but because it strives for simplicity, it might be useful for people interested in learning about OS kernel implementation.
Note that the development of GeekOS is slow. If you are interested in working on it, send me an email.