In Gemfile:

    gem 'figgy'

Configure (say, in a Rails initializer):

    APP_CONFIG = Figgy.build do |config|
      config.root = Rails.root.join('etc')

      # config.foo is read from etc/foo.yml
      config.define_overlay :default, nil

      # config.foo is then updated with values from etc/production/foo.yml
      config.define_overlay(:environment) { Rails.env }
    end

Access it as a dottable, indifferent-access hash:

    APP_CONFIG["foo"]["some_key"]
    APP_CONFIG[:foo].some_key
    APP_CONFIG.foo[:some_key]