Here is a short collection of current Content Management Systems (CMS) written in Ruby and mostly suited to use with Ruby on Rails. Check out Ananablau as well for a nice PDF slide.

Comatose (29. June 2007)
Comatose is a micro CMS designed for being embedded into existing Rails applications
http://railsbased.org/projects/8-Comatose.html

Geego
Geego is for developers and designers that want to provide fully updatable websites for their clients.
http://www.geegocms.com/

Mephisto (27. July 2006)
Complete Blog System, Mephisto is a publishing system that makes it super easy to setup a blog or website.
http://mephistoblog.com/

Typo
Complete Blog System, Similar to Mephisto
http://wiki.github.com/fdv/typo/

Radiant CMS
Radiant is a no-fluff, open source content management system designed for small teams.
Looks cool but no direkt RoR integration?
http://radiantcms.org/

Railfrog (3. July 2007)
Railfrog is a user-friendly, open-source website deployment and content management system built with Ruby on Rails.
dead project?!
http://railfrog.com/

Rubricks (31. July 2007)
Rubricks is a component based open source CMS powered by Ruby on Rails.
http://rubricks.org/

Seymore (04/02/2007)
Seymore is an open source content management system which integrates directly into pages.
http://www.slicedsoftware.com/software/seymore/

SimpleCMS , (29. December 2007),
small simple, inline edit. Simple CMS is a very easy to use and pretty advanced CMS plugin.
http://pullmonkey.com/2007/12/30/simple-cms-plugin-for-rails-demo

CMSPlugin
CMSplugin provides your Rails application with a “CMS framework”. That means authentication, authorization, roles, permissions, categories, tags, etc… but from a very flexible scope.
http://cmsplugin.rubyforge.org

open rcms (25.6.2007)
http://rcms.oopen.de/Home/

Roxanne
An in-place editor for your entire website. Roxanne is a simple Site-Management Tool to quickly manage your content. See first steps to get the idea behind Roxanne.
http://www.m42.ch/projects/roxanne/information.php

Substruct
The first and most robust Ruby on Rails open source e-commerce project.
http://code.google.com/p/substruct/

Goldberg (promising)
http://www.goldberg.240gl.org