> it seems that qt is the only option that includes GUI 
> code designer (with signals etc). I did try wxruby but couldn't find a 
> helper application that would allow this.

Just for the record, you can use any of the numerous free and commercial RAD designers for wxwidgets with wxRuby:

http://en.wikipedia.org/wiki/WxWidgets#IDE_and_RAD_tools

Save the GUI design as an XRC (xml) file, and then you can load it into ruby - see the xrc sample in samples distributed with wxruby.

alex