Jonathan Jacobs has released a set of modules to "hack" Appleis latest OS release, 9.1. Jonis OS 9.1 Mods are a collection of ResEdit files that allow users to change the basic behavior of some aspects of the OS. According to Mr. Jacobs:
It is a collection of ResEdit modifications that add key commands to the Finder, enlarge old-style Open/Save dialog boxes, adds the ability to windowshade QuickTime and Sherlock windows, and more.
Jonis OS 9.1 Mods are available for free. You can find more information at the OS 9.1 Mods page.