From Fedora Project Wiki
Ruby on Rails
Fedora 21 includes Ruby on Rails 4.1, the latest version of the well-known web application framework written in Ruby. Highlights in this release include Spring application preloader, config/secrets.yml, Action Pack variants and Action Mailer previews. The Release Notes are at [1].
Information for developers upgrading existing applications to Ruby on Rails 4.1 can be found in the Upgrading Ruby on Rails guide at [2].