title: Mobile app - Push notifications alternatives?
body: <p>I need push notifications for my app, is GCM the only way to go?
  And is GCM only available via Appengine (and Firebase)?</p>
  
  <p>Or can you use it on Heroku and other services?</p>
  
  <p>Is it a big no to use polling or implement your own push notification srvice (which uses polling anyway)?</p>
  
  <p>Does GCM work for iOS?</p>