There are a number of other GUI toolkits under development for Ruby, and as always, you should check the RAA for the latest word.

The Fast Light Toolkit (FLTK) (www.fltk.org) is a nice cross-platform GUI developed in part by Bill Spitzak. FLTK is very efficient in terms of memory use and speed, and provides excellent support for OpenGL-based applications as well. It is currently available for both Windows and X (Unix) platforms. A Ruby interface to FLTK is being developed by Takaaki Tateishi and Kevin Smith, and the home page for this effort is at http://ruby-fltk.sourceforge.net.

Qt (www.trolltech.com) is an excellent cross-platform GUI toolkit that has been ported to Unix, Microsoft Windows and, most recently, Mac OS X. It is the basis of the popular KDE desktop for Linux. The Ruby language bindings for Qt (http://sfns.u-shizuoka-ken.ac.jp/geneng/horie_hp/ruby/index.html) are developed by Nobuyuki Horie.

Apollo (www.moriq.com/apollo/index-en.html), developed by Yoshida Kazuhiro, is a project whose goal, in the author's words, is to provide a "dream duet" of Delphi and Ruby. Delphi is a commercial application development environment from Borland/Inprise. The specific interest for Ruby GUI developers is in the Ruby extension that provides access to Delphi's Visual Component Library (VCL). As of this writing, Delphi is only available on Windows, but very soon, Kylix (the Unix port of Delphi) should be available for Linux and other platforms.