Setler is a Gem that lets one easily implement the "Feature Flags" pattern, or add settings to individual models. This is a cleanroom implementation of what the 'rails-settings' gem does. It's been forked all over the place, and my favorite version of it doesn't have any tests and doesn't work with settings associated with models.
Gemfile gem 'setler', '~> 0.0.6'
install gem install setler -v 0.0.6