From pnppl.cc:
https://pnppl.cc/

Code is licensed AGPLv3:
https://www.gnu.org/licenses/agpl-3.0.en.html

Other content is licensed CC BY-SA 4.0, with attribution waived:
https://creativecommons.org/licenses/by-sa/4.0/

In plain English: do whatever you want with this, but anything you make with it must use the same license. This ensures that others can also do whatever they want.