The link is to a course in operating system design and implementation that uses a simple kernel based on a historically relevant UNIX. The simple kernel has been updated to take advantage of a relatively new architecture (RISC-V) that was developed academically (but has actual industrial chips and boards that you can buy and run).
It's great pedagogically because the kernel is simple, well-architected, and excellent for undergrads to work with. Historically, academic UNIX has been tremendously useful for development of new concepts, as well as teaching the next generation.
Some notes of interest:
1) all-around genius Russ Cox is one of the developers and teacher for the course.
2) another teacher is Robert Morris Jr, who developed the sendmail worm back in the day. He is now a professor at MIT.
9
4