The primary Trilinos repository is now hosted on GitHub. Contributions can be offered through the standard GitHub pull request model. We strongly encourage you to coordinate large contributions with the Trilinos development team early in the process. One way to do this is to file a ticket in the GitHub issue tracking system prior to any code development.
The Trilinos Project welcomes contributions from new developers, but we ask that you complete and submit a contributor agreement. There are two versions of the agreement, one for individuals, and one for organizations. Please look at both to determine which is right for you.
If you are thinking about contributing, you may want to subscribe to our mail lists.