Ruby Gui

There several ways in which to provide a graphical interface for the RubyLanguage.

RubyTk
Ruby/GTK
FX/Ruby (FOX)

The above are described in some detail in Chapter 6 of TheRubyWay. In addition, there are

JavaSwing or JavaSwt when using JayRuby
RubyShoes, which is new in the field

See also

http://wiki.rubygarden.org/Ruby/page/show/ComparingGuiToolkits for a comparison
ThenDontCallMainLoop which has an example using Ruby/GTK.