Lustr is a Ruby DSL for GUI apps. Write a Lustr GUI once, and you can run it with Ruby controllers on the desktop (using wxRuby or JRuby/Swing) and run a code generator to convert the UI to Flex/MXML or XUL, to tie into your AS/JS controllers.

Lustr 0.1.0, the initial release, has been published as gems to its RubyForge project. More info can be found at the Lustr portion of the CodeCorps wiki: http://www.codecorps.org/moinmoin/index.cgi/Lustr