The December Developer Tools download and mailing contains AppleScript Studio, previewed earlier this year to great reviews.
This story originally stated that the tools were available for general download by any registered developer (including free online-only developers). Unfortunately, this appears not to be the case. I had followed a link off the VersionTracker page, logged in, saw the tools, and assumed they were being generally distributed. This was an incorrect assumption on my part. At this point, it appears that only those developers who receive the Developer Tools' mailings on CD-ROM have the ability to download the December release which includes the AppleScript Studio.
UPDATE:
Quoting Apple: "The December 2001 Mac OS X Developer Tools will be available as a free download or for purchase on CD-ROM from the ADC Member Site during the week of December 10. All ADC Online members will be notified via email when the Tools become available."
Mac OS X Hints
http://hints.macworld.com/article.php?story=20011205014730356