Google Toolbox For Mac: http://code.google.com/p/google-toolbox-for-mac/
A collection of source from different Google projects that may be of use to developers working other Mac projects.
Includes classes for doing a variety of things at both the Foundation and AppKit level on both the MacOS and the iPhone.
Also has a full set of classes for doing UnitTesting of user interfaces, bindings, etc.
All licensed under the Apache2 license.