I am not a lawyer or any kind of expert on software licensing, but even I can see that there's a lot of grey area where SS13's licensing is concerned. This is how the original code is licensed:
All code after commit 333c566b88108de218d882840e61928a9b759d8f on 2014/31/12 at 4:38 PM PST (https://github.com/tgstation/-tg-station/commit/333c566b88108de218d882840e61928a9b759d8f) is licensed under GNU AGPL v3 (http://www.gnu.org/licenses/agpl-3.0.html).
All code before commit 333c566b88108de218d882840e61928a9b759d8f on 2014/31/12 at 4:38 PM PST (https://github.com/tgstation/-tg-station/commit/333c566b88108de218d882840e61928a9b759d8f) is licensed under GNU GPL v3 (https://www.gnu.org/licenses/gpl-3.0.html). (Including tools unless their readme specifies otherwise.)
See LICENSE-AGPLv3.txt and LICENSE-GPLv3.txt for more details.
tgui clientside is licensed as a subproject under the MIT license. tgui assets are licensed under a Creative Commons Attribution-ShareAlike 4.0 International License (http://creativecommons.org/licenses/by-sa/4.0/).
See tgui/LICENSE.md for more details.
All assets including icons and sound are under a Creative Commons 3.0 BY-SA license (http://creativecommons.org/licenses/by-sa/3.0/) unless otherwise indicated.
I guess it's best to assume the following:
- Code is licensed under AGPLv3 -- See LICENSE-AGPLv3.txt for details.
- Some assets have their own specific licenses, but they live in their own repositories so they're not my problem.
For the record, I do not approve of this bullshit. If I had my way, all new changes would be licensed under MIT or WTFPL, but it has come to my attention that this might not be okay. I don't really care if this is okay, but I'll deal with the AGPL it if it helps avoids a shitshow.
Please contact me if you have concerns or suggestions regarding the license.