AssaultCube Special Edition
AssaultCube Special Edition is released under the GNU General Public License version 3 (GPLv3)
The code is licensed under the zLib licence, allowing this modification.
A nice statement from them: "The entire AssaultCube package MAY be redistributed"
In addition to that: the packages inside of it allows it to be used for non-commercial uses.
Disclaimer: They updated their licence, but the above was factual before it was changed.
Irrelevant; this is an AssaultCube mod. Their relationships with Cube are not "in our jursdiction".