http://www.laszlosystems.com/
In a nutshell, it's a compiler that takes JavaScript code embedded in XML (which is somewhat XUL/XAML-like), and compiles it down to Flash, which you can run in your browser.
And it's now open source.
Sad part is that it requires J2EE or something to run the compiler, but I'm not sure you need that past compiling it the first time. That is, I'm not sure if the data access components need the J2EE bit or not. If so, maybe I can reproduce that part of the server in Perl, so I can comple Flash apps once, then deploy them with a perl dataserver.
Check it:
http://www.laszlosystems.com/demos/
Or use their compiler live:
http://www.laszlosystems.com/lps/laszlo-in-ten-minutes/
Very, very sweet.
In college I once wrote a Java Applet that let you program robot tanks in Lisp (with syntax highlighting), sent the Lisp across the network to a Perl server which compiled it to Java bytecodes, then dynamically loaded the tank class files and it drove around a battlefield, fighting other tanks, based on the Lisp code.
OpenLaszlo has that same sort of hack value to it, but it actually looks useful.