Gemfile

source :gemcutter
gem 'sinatra', '1.2.1'
gem 'thin', '1.2.11'

Gemfile.lock

GEM
  remote: http://rubygems.org/
  specs:
    daemons (1.1.2)
    eventmachine (0.12.10)
    rack (1.2.2)
    sinatra (1.2.1)
      rack (~> 1.1)
      tilt (>= 1.2.2, < 2.0)
    thin (1.2.11)
      daemons (>= 1.0.9)
      eventmachine (>= 0.12.6)
      rack (>= 1.0.0)
    tilt (1.2.2)

PLATFORMS
  ruby

DEPENDENCIES
  sinatra (= 1.2.1)
  thin (= 1.2.11)

Procfile

web: bundle exec ruby web.rb -p $PORT

web.rb

require 'sinatra'

get '/' do
  'hello'
end