cosmopolite

See https://www.cosmopolite.org/ for tutorial, reference, etc.

Client/server publish/subscribe and key/value storage for AppEngine.

Components:

Feature overview:

Near-realtime notification to subscribers of messages published to a "subject"
Server-side storage of past messages for replay later to clients
Support for associating a key with a message and for lookup of the most recent message for a given key
Client identification persistence via localStorage tokens or in combination with Google account signin
Complex messages supported via transparent JSON serialization
Server-side strict ordering of messages
Client-side message queueing in localStorage and resumption on restart
Message duplication detection and elimination
Promise support for notification of client -> server operation completion