If you're like me and don't care about non-Google devices and would rather not have yet another background service running, you can easily send GCM notifications from CloudCode.

gistfile1.txt

Parse.Cloud.httpRequest({
  method: 'POST',
  url: 'https://android.googleapis.com/gcm/send',
  headers: {
    'Authorization': 'key=' + GCM_API_KEY,
    'Content-Type': 'application/json'
  },
  body: {
    registration_ids: gcmRegIds,
    data: {
      // Put something here
    }
  },
  success: function(httpResponse) {
    // Do something
  },
  error: function(httpResponse) {
    console.error('GCM Request failed' + JSON.stringify(httpResponse));
  }
});

port 8253