Apple just released AppleScript Studio in the December 2001 Developer Tools update! Get it from Apple.
If you haven't heard of it, AppleScript Studio is Apple's integration of a few technologies. First, they extended Project Builder to edit, format, color, and debug AppleScripts. Then, they wrote a terminology dictionary to give AppleScript the ability to manipulate Cocoa objects. Finally, they modified Interface Builder to allow the developer to hook up a Cocoa widget with an AppleScript "handler".
Several of us at my company have been eagerly awaiting this release. It's an interesting hybrid application of all the technologies Apple now controls -- some Apple projects, and some NeXT projects. Also, it seems to revive a lot of the missing rapid development possibilities left untapped by the demise of HyperCard -- all that is missing is an Object Database.
More to come as I explore the possibilities embodied in this exiting new release.