I'll say a few words about this most excellent program that others, including the author, hasn't said, at least on this page.
This program works by reading a simple text file which you the user (programmer) set up. Thus, it can be used by _any_ language that can read and write text files, which is pretty much any language that you can think of. (The author does mention this in the documentation.) That means not just script languages but any language. I use it from Ada--there is no reason that you can't use it from your favorite language(s).
It's actually pretty amazing to see a nice Cocoa interface appear for your "command line interface" language with just a little effort. No, you can't write arbitrary GUI programs, but it will get you a lot of GUI for not much effort. This program has been around for a few years (most of OS X's life) but the author is supportive and really, there's not really much need to release frequent updates as "it just works." Yes, it is similar in ways to Cocoa Dialog but still has features that the others don't.