I'm looking for a substitute for Wordpress and Squarespace that's implemented in Ruby. It can be a Rails app, a Rails plugin, or a standalone static page generator. The most important features we're looking for is that it comes with a selection of nice looking themes and is easy to set up.
I've used Typo in the past with success. It's written in Ruby, is reasonably active and can be installed as a gem. It comes with a default theme and there are a bucket full of themes available at Typogarden.