The latest MINUX version is 3, and is released under the BSD license.

http://www.minix3.org/

Minux is relevant still, because it teaches bozos like the Linus Torvalds a little about software engineering, just as Algol and Oberon teaches C programmers a bit about software engineering (but Minux still sucks balls, and Oberon blows as it doesn't get strings right, and never has).

Looking into the Plan 9 (from bell labs) source code... I can say it is the exact opposite of MINUX. Plan 9 is written without comments (except in the assembly code files) and poor function names/variable names were chosen. Okay, Plan 9 is still pretty cool, and Acme is cool, but.. the source code just doesn't have much explanation because they believe the source code is the source code, and it needs no explanation.