Bourbon is a set of Sass mixins using SCSS syntax
Copycat is a Rails engine that allows editing live website copy using existing i18n view helpers
Easy file attachment management for ActiveRecord
rails-bootstrap-forms is a Rails form builder that makes it super easy to create beautiful-looking forms with Twitter Bootstrap 3+. Wraps the standard Rails form helpers so it's practically a drop-in replacement.
Simple, link-based conversion tracking--it's like a URL shortener with awesome analytics. Use it to track traffic and conversions for any link anywhere (mobile, social, email, web, etc.)
Webrat - Ruby Acceptance Testing for Web applications