Developer Resources (2.10.1)
To learn how to make Nimbus components behave differently (beyond configuration), see the Extensibility Guide.
To learn about source control, including where to view the source online, see Source control.
To learn how the release process is structured, see the Release Policies and Procedures wiki page.
You can contribute without a vote to bring you in as a full committer and many do. All that is necessary is that you sign a contributor's license which allows us to freely distribute your contributions. Your git author information is preserved in the repository, you just don't have free reign in this situation.
You will get access to the Nimbus contributor chatroom and any amount of praise and encouragement you can handle :-)
The best place to "dive in" to working with Nimbus (whether it be to contribute something or to customize something for your own purpose) is by learning to run the test suites. Run some of the unit suites. Change some behavior and run them again and see what happens. Try it with the debugger and step through how some of the code flows. Make a quick contribution by writing a new test!