Everyone here knows what Multics was and when it was made?
How many people know when the last Multics system went down forever?
How Many people have the source code for Multics?
http://web.mit.edu/multics-history/
[ note: wget is your friend if you want to get the sources ]
Yes, the original operating system that inspired unix is now public domain, with only acredidation required for any use whatsoever.