A demo App Engine server using https://w3c.github.io/push-api/ to send push messages to web browsers.
Live version: https://jakearchibald-gcm.appspot.com/
Currently requires Chrome 42+. Other browsers will be added as the implement the Push and Notifications APIs (Firefox Nightly already has partial support).
See requirements.txt for instructions on installing dependencies, if you want to run your own copy on App Engine.