This game uses the Shoes framework. It was developed on Mac, but should also work on other platforms (Linux, Windows).
To run the game, first install Shoes 2 (this includes Ruby with it).
After you do that, run tictactoe_shoes.rb using Shoes.
The game was developed test-first using rspec tests against a test engine. The tests are are in tictactoe_spec.rb and you can run them if you have rspec installed.
The tictactoe.rb file itself is pure Ruby and does not use Shoes itself.