I had good success with qtruby. Qt is the toolkit underlying KDE and it
is available for Windows.
It is free for non-commercial use. Please read the license to see if it
fits your requirements. http://trolltech.com/products/qt
I really like that toolkit - it have a very nice and comfortable GUI
editor (Glade), is very good integrated in Ruby with Gnome2-Ruby and
easy to learn. But for windows it’s not the best I think: Yes, it works
with windows. But it’s not really well integrated. Do you use Pidgin,
Gajim, Gimp or something like this (All those application use GTK) with
Windows? If yes I think you know what I mean.
Also it’s not really fast when you use windows cause you have to load
GTK which is within Linux with Gnome already done.
I think wxRuby is bether for multi platform compatibility and native
look and feel also for Mac OS X. But I was unable to find a GUI editor
which is so good as the Glade of GTK and it was more difficult for me to
understand it as an beginner. Maybe it’s the best to try both or these
both and more like FxRuby etc.