You'll need ruby and redis installed to run this. If you're on a mac, one way to go getting redis is to install homebrew, then run brew install redis. Then, for ruby, install rvm.
Once ruby + redis are installed you can just run redis-server in a terminal to start redis.
To boot the ruby web server that serves our html + css:
bundle install
bundle exec puma
Now you should be able to just visit localhost:9292 in your browser to see the chat. Open it in a few windows to chat between them!
The web server tries, by default, to talk to redis using its default settings. If you need to specify different redis config details, create a .env file containining REDIS_URL=redis://somehost:someport. Alternately, provide REDIS_URL as an environment variable when running puma, like REDIS_URL=redis://somehost:someport bundle exec puma.