Sinatra 1.0, a micro-web framework, is having a bit of trouble with Ruby 1.9.2. Your apps just won't run, you get no output and the interpreter returns to the shell with no exceptions thrown. This (presumably) will be fixed in the next version of Sinatra, but there's a temporary workaround, and it only requires you to add a single line to your application. The line is highlighted below.
#!/usr/bin/env ruby require 'rubygems' require 'sinatra' enable :run get '/' do "Hello, world!" end