Make sure to intsall the colorize gem in order to use this version of checkers. http://colorize.rubyforge.org/files/README_txt.html
If you want to use checkers.rb (instead of checkers_plain.rb), install the everson font and use it in your terminal. Find it here: http://www.evertype.com/emono/
To run the program, download the .rb files and type "ruby checkers.rb" or "ruby checkers_plain.rb" in your terminal.
Enjoy!