The simplest Rails app (inspired by http://railscasts.com/episodes/349-rails-modularity)

config.ru

require "action_controller/railtie"

class TheSimplestRailsApp < Rails::Application
  config.secret_token = "ef224177dc6ddcaabffafdbaa50cdb173eb744932073d"
  config.eager_load = false
  initialize!

  routes.draw do
    root to: "hello#world"
  end
end

run TheSimplestRailsApp

class HelloController < ActionController::Base
  def world
    render inline: "hello world"
  end
end

# start with `$ rackup` and visit localhost:9292