All Aimy Extensions are open source.
The (PHP) code of all extensions is released under the terms of the GNU General Public License Version 2 (GPLv2), a both popular and widespread open source license.
All translations are done under the terms of the Creative Commons Public Domain Dedication License Version 1.0 (CC0 1.0).
You'll find a copy of the license terms within every Aimy Extensions package ("LICENSE.txt" / "LICENSE-I18N.txt"). You may also read the licenses online, for example at: http://www.gnu.org/licenses/gpl-2.0.html and https://creativecommons.org/publicdomain/zero/1.0/.