modular sinatra app taken from here => https://github.com/jfeaver/modular-sinatra/

app.rb

class Datafruits < Sinatra::Base
  @@my_app = {}
  def self.new(*) self < Datafruits ? super : Rack::URLMap.new(@@my_app) end
  def self.map(url) @@my_app[url] = self end

  # do all config stuff in this file
  enable :sessions
  use Rack::Flash

  class ApplicationController < Datafruits
    map '/'
  end

  class SessionsController < Datafruits
    map '/'
  end
  class UsersController < Datafruits
    map '/users'
  end
end

application_controller.rb

class Datafruits
  class ApplicationController
    get '/'
      erb :index
    end
  end
end

boot.rb

dir = File.expand_path("../", File.dirname(__FILE__))

require "#{dir}/app"
app_dir =  File.join("#{app_dir}", "app/")

controller_files = File.join(app_dir, %w(controllers ** *_controller.rb))
model_files = File.join(app_dir, %w(models ** *.rb))
lib_files = File.join(dir, %w(lib ** *))

files = [controller_files, model_files, lib_files]

Dir.glob(files).each {|lf| require lf }