Professor, Free University, Amsterdam; author of MINIX Unix variant. Full source code. Free for all uses. Small size, microkernel, ample documentation. Users unfamiliar with OS internals can understand nearly the full system with a few months use and ...
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.
Unix clone that is free, small, flexible, secure, and self-healing, leading to high reliability, even during software faults. Descriptions, FAQ, book, newsgroup, screenshots, bug reports, downloads. [open source, BSD-like]
Line-by-line comments of source code for TCP/IP networking protocols, network service, for Minix version 2.0.4. By Christos Karayiannis, Andrew Swartzbaugh.