Like OKCupid, but for finding roommates
http://roominate.herokuapp.com
To demo the app, you can sign up or log in as a seed user, using the username "userXX" where XX is any number from 1 to 200, and the password "123." Find some matches, send them notifications and log in as them to demo receiving a message.
If the above image link is broken, you can view the demo here.