CommunityEngine is a free, open-source social network platform for Ruby on Rails applications. Drop it into your new or existing application, and you’ll instantly have all the features of a basic community site.

Rails 3.1 drop-in blog engine for existing Rails applications

Blog engine for Rails 3.1+

Forgeos Blog provide papers (blog posts), comments and tags management

Georgia::Mailer works essentially with Georgia CMS to provide spam-free contact forms, email notifications, Sendgrid integration, and so on.

Comments plugin for the Rails 3-based Governor blogging system.

A plugin for the Rails 3-based Governor blogging system that enables you to tag your articles.

Parlez is french for 'Speak!'. It's also a blog which is also a Rails 3 Engine.