Professor Andrew S. Tanenbaum's famous UNIX clone. Full source code. Free for education or research use. Small size, microkernel-based design, ample documentation. A user unfamiliar with OS internals can understand nearly the entire system with a few mont http://www.cs.vu.nl/~ast/minix.html
MINIX that runs atop Mac OS. Benefits: while learning about operating systems, its easy to recompile and relaunch, with no rebooting; and to keep OS backups in separate files. http://www.pliner.com/macminix/
Major resource providing information about the Minix operating system, downloads of Minix and contributed software for Minix. http://minix1.hampshire.edu/
Repository for OS related: documentation, help, information, news, links, books, source code, downloads. Not the official MINIX website. http://www.minix.org/