Back before Linux was a gleam in Linus's eye, there was a UNIX-like system called MINIX. Created by Andrew Tanenbaum, MINIX was a micro-kernel based system that was built for the purpose of learning about operating system design in universities. In fact, MINIX is one of the original reasons that Linux was first created. In those early days, Tanenbaum and Torvalds had some great, no-holds-barred exchanges, resulting in some of the following quotes from the MINIX creator.
"LINUX is obsolete."
"Be thankful you are not my student. You would not get a high grade for such a design :-) ... Writing a new OS only for the 386 in 1991 gets you your second F for this term."