appengine-java-sdk => http://code.google.com/appengine/downloads.html
git clone git://github.com/jugyo/sinatra_on_gae.git
dev_appserver.sh ./sinatra_on_gae
Edit appengine-web.xml:
...
<application>[Your Application Identifier]</application>
...
Run a command:
appcfg.sh update ./sinatra_on_gae