MINIX is a Unix-like computer operating system based on a microkernel architecture created by Andrew S. Tanenbaum for educational purposes; MINIX also inspired the creation of the Linux kernel.
MINIX (from "mini-Unix") was first released in 1987, with its complete source code made available to universities for study in courses and research. It has been free and open source software since it was re-licensed under the BSD license in April 2000.
Read more about MINIX: MINIX and Linux, Licensing