SpongeForge, SpongeVanilla, SpongeCommon, and the Sponge API are licensed under the MIT licence. There is no contributor licence 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 licence is an extremely permissive licence, 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 licence, especially when considering the fate of other projects with goals similar to those of Sponge. The licence offers peace-of-mind in ensuring Sponge has a bright future. Further details on the licence can be found at https://choosealicense.com/licenses/mit/.
The SpongeDocs are licensed differently under the Creative Commons - Share-Alike licence.
Art assets are held under the Creative Commons - Non Commercial, No Derivatives licence.
Contributions to the projects implicitly accept their respective licences.