QARoR
Questions & Answers platform on Rails - stackoverflow clone http://qaror.herokuapp.com/
https://github.com/mateuszdw/qaror
Fairnopoly
Fairnopoly is a free market place in the hand of the users. https://www.fairnopoly.de/
https://github.com/fairnopoly/fairnopoly
Scumblr
Scumblr is a web application that allows performing periodic searches and storing / taking actions on the identified results.
https://github.com/Netflix/Scumblr