"The sources for the Multics timesharing operating system have been donated to MIT by Group Bull. They are published under a BSD-style license, apparently. As noted on the site, the sources have only been preserved because they were saved on a DAT before the shutdown of the last Multics system running in CGI (Calgary, Canada)."
http://web.mit.edu/multics-history/source/Multics_Internet_Server/Multics_sources.html