Bidirectional messaging over HTTP, one concrete implementation based on the bidi-web semantics.
Platform neutral Java client (API and protocol spec): client/java/bidiweb/webchannel
Closure JS API spec: https://github.com/google/closure-library/blob/master/closure/goog/labs/net/webchannel.js
Open-source Go server: https://code.taxi/samegoal/wc
Shared whiteboard Demo: https://webchannel.sandbox.google.com/static/whiteboard.html