This is what I use as a template for my Sinatra applications.
Parts of the code were inspired by the work of Raf and Étienne at Heliom.
$ git clone https://github.com/remiprev/sinatra-kickstart.git
$ cd sinatra-kickstart
$ bundle install
$ bundle exec shotgun start --host 0.0.0.0
== Shotgun/Thin on http://0.0.0.0:9393/
>> Thin web server (v1.5.0 codename Knife)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:9393, CTRL+C to stop