Firefly is a light-weight URL Shortener app. It's written in Ruby/Sinatra and can be easily deployed to Heroku, as I've written before. This screencast illustrates how easy it really is to setup Firefly and give it a spin. Did I mention that both Firefly and Heroku can be used for free?
~ As always I'm keen to hear how you are using Firefly. Got some coding talents? Feel free to contribute features and fixes through github.