Any success with Sinatra working together with EventMachine WebSockets?

Did not try it, but should not be too hard:

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

EM.run do
  class App < Sinatra::Base
    # Sinatra code here
  end

  EM::WebSocket.start(:host => '0.0.0.0', :port => 3001) do
    # Websocket code here
  end

  # You could also use Rainbows! instead of Thin.
  # Any EM based Rack handler should do.
  Thin::Server.start App, '0.0.0.0', 3000
end

Also, Cramp has a websocket implementation that works directly with Thin/Rainbows! you might be able to extract, so you won’t even need to run the server on another port.