I was reading the Apple document “Cocoa Fundamentals Guide” and ran across some nice class hierarchy charts for Foundation classes that I thought I’d share. They are located in the section of the document called “What Is Cocoa?“.
These diagrams logically group the classes of the Foundation framework in categories. Classes in blue-shaded areas are present in both the OS X and iOS versions of Foundation; classes in gray-shaded areas are present only in the OS X version.
Click on an image for the full size representation.