ZOMG_GAMES is a project mainly written in Ruby, it's free.
Writing games with Ruby (RubyConf 2010)
Writing games with Ruby
RubyConf 2010 Mike Moore November 13, 2010
The first example game demonstrates moving objects on the screen.
ruby demo_game.rb
The second example creates an animated sprite that you can control.
ruby sprite_game.rb
The third example demonstrated clipping and simple game mechanics.
ruby patrol_game.rb
The last example is a mostly working game where you avoid ev1l snakes so you can attend RubyConf.
ruby rubyconf_game.rb