Eribium is a open source content managing editor, built with Ruby on Rails.
under development: Railfrog is a user-friendly, open-source website deployment and content management system built with Rails
Pimki is a wiki-based PIM to GetThingsDone!. Loosely based on Instiki's Wiki technology (http://www.instiki.org) and with strong GTD influences, Pimki is aimed at being a light-weight, flexible organiser for all the various bits and pieces of your life.
Radiant is a no-fluff, open source content management system designed for small teams.