I just wanted to pass on the meme on a great RoR-based CMS - Radiant. It is OSS, very stable, fairly actively developed and has a really good plugin system.

While searching for a RoR-based CMS I looked at it a few others:
Mephisto

• Development has dried up due to the developers not having the time to continue it.
• No support for snippets (see below).

RailFrog