Minux is an operating system written by AndrewTannenbaum for "Operating Systems: Design and Implementation". Linus and AndrewTanenbaum had a FlameWar over the various design decisions.
Before Linux became popular, Minix was widely used for teaching unix internals at universities, due to its available source code (although not under what we would call a Free license these days), clean implementation, and general "smallness" or lack of bloat (and functionality). It made (makes?) wide use of message passing, so students can trace the chain of functions called to perform a particular task.
See also MinixFS, MinixNotes.
My first introduction to Unix was by reading that book. -- PerryLorier
JohnMcPherson and StuartYeates had to use Minix in a unix-related course at CanterburyUniversity as late as 1998, well after Linux was widely used. Fortunately, they got over the experience.
Writing an extension to the Minix kernel was also an assignment for the course COMP301 (OperatingSystems) at WaikatoUniversity in 2005 and 2006.
Comp301 was a horrible Java concepts class in 2008, but I am led to believe it is back to minix this year (2009). 4/501 is doing a minix related course for 2009 as well, and it rocks! --ShaneHowearth
Comp301 is back to a majority minix based cause, who ever thought of using Java for operating systems yesh, hope they keep it to minix for next year -- Ronnie Collinson