Below are links to the Quicksilver source, and the plugin source. You can also find information on how to develop plugins for Quicksilver.
If you've had a play with Quicksilver's source code, and are interested in helping develop Quicksilver then please post in the Quicksilver Developers Google Group
When releasing a new version, a certain Release Process should be followed, to make sure no important steps are missed.
If you'd like to help run, manage or contribute to this website, see the QSApp.com page.