SpongeForge, SpongeVanilla, SpongeCommon, and the Sponge API are licensed under the MIT license. There is no contributor license agreement, and all contributions to the Sponge projects are welcome. We also explicitly grant permission to distribute SpongeForge in any third-party modpack.
The MIT license is an extremely permissive license, placing almost no restrictions on what can be done with Sponge. The only requirement is that the copyright header must be left intact.
There is true value in licensing Sponge under the MIT license, especially when considering the fate of other projects with goals similar to those of Sponge. The license offers peace-of-mind in ensuring Sponge has a bright future. Further details on the license can be found at https://choosealicense.com/licenses/mit/.
The SpongeDocs are licensed differently under the Creative Commons - Share-Alike license.
Art assets are held under the Creative Commons - Non Commercial, No Derivatives license.
Contributions to the projects implicitly accept their respective licenses.