The initial Plan 9 code has been received, modified and is redistributed according to the GNU General Public License, Version 2 as explained in /doc/licence/LICENSE.Plan9.txt.
The kernel is a direct fork of Charles Forsyth's Plan9-9k, according to /doc/license/NOTICE.Plan9-9k.txt. Original kernel code is released as GNU General Public License, Version 2.
New tools and improvements ported from 9front are subject to the MIT license as explained in /doc/licence/9front-mit.txt.
New libraries and programs that use Plan9 libraries as system libraries can be subject to different licenses, as documented in the respective sources.
New System Libraries
Some new libraries designed for use within Jehanne are released under GNU Affero General Public License, Version 3.
They can be linked as "System Libraries" for use within Jehanne.
Jehanne contains a number of third-party packages under various licenses.
They are retrieved from their respective sources - licenses for these packages are not included here, but should be available from the respective directories in /sys/src, /pkgs or /hacking.