This project is published under the Creative Commons Attribution-ShareAlike 4.0 International License. I think that this is the best license for community-driven creative projects (the GPL is best for software). To quote the Creative Commons website:
This license lets others remix, tweak, and build upon your work even for commercial purposes, as long as they credit you and license their new creations under the identical terms. This license is often compared to “copyleft” free and open source software licenses. All new works based on yours will carry the same license, so any derivatives will also allow commercial use. This is the license used by Wikipedia, and is recommended for materials that would benefit from incorporating content from Wikipedia and similarly licensed projects.
You should have received a copy of the license along with this work. If not, see https://creativecommons.org/licenses/by-sa/4.0