OWASP SAMM has moved to a new organization: https://github.com/owaspsamm. There you will now find both the core model as well as all derived projects.
If you're looking for documents related to OWASP SAMM, you can find them in the project's Google Drive.
This repository has been archived. You can still browse all the historical information up until and including the version 2.0 here, however all the new development is taking place in the new org.