Tetrubyis is a project mainly written in Ruby, it's free.
Tetris clone written in Ruby with SDL
Tetris Clone written in Ruby using SDL.
sudo port install libsdl libsdl_gfx libsdl_image libsdl_mixer libsdl_ttf bundle install --path vendor
On Snow Leopard and Lion you may need to run env ARCHFLAGS="-arch x86_64" bundle install --path vendor