RethinkDB - Open-Source DB for the Realtime Web

RethinkDB is an open source database for the real-time Web. It has a built-in change notification system that streams live updates to your application. Instead of polling for new data, you can have the database push the latest to changes to you. The ability to subscribe to streaming updates from the persistence layer can simplify your application architecture and make it easier to support clients that maintain persistent connections to your back end."

https://github.com/rethinkdb/rethinkdb

https://www.rethinkdb.com/

https://horizon.io/

http://www.infoworld.com/article/2975838/database/build-real-time-web-apps-with-rethinkdb.html