app.rb

require 'rubygems'
require 'em-websocket'
require 'sinatra/base'
require 'thin'

class App < Sinatra::Base
  get '/' do
    return "foo"
  end
end

EventMachine.next_tick do
  EventMachine::WebSocket.start(:host => '0.0.0.0', :port => 8080) do |ws| # <-- Added |ws|
    # Websocket code here
    ws.onopen {
        ws.send "connected!!!!"
    }

    ws.onmessage { |msg|
        puts "got message #{msg}"
    }

    ws.onclose   {
        ws.send "WebSocket closed"
    }
  end
end

App.run!({:port => 3000})