This is a barebones Ruby app using the Sinatra framework.
Asumming you have Ruby, Bundler and Heroku Toolbelt installed on your machine:
git clone git@github.com:heroku/ruby-sample.git # or clone your own fork
cd ruby-sample
bundle
foreman start
Your app should now be running on localhost:5000.
heroku create
git push heroku master
heroku open
For more information about using Ruby on Heroku, see these Dev Center articles: