Engrave
No, the world does not really need yet another Ruby blogging engine.
Installation
# Gemfile
gem 'engrave'
# Don't forget
$ bundle install
# Setup the DB
$ rake engrave_engine:install:migrations
$ rake db:migrate
# Create a Post
> Page.new( { :name => "First Page", :body => "Here is some **markdown** baby!"} )
Now go visit http://myserver/pages/first-page