A fully managed database agnostic GraphQL service for building modern applications with first class support for real-time and offline.
Check out projects like Conference in a Box which uses AppSync to deliver real-time comments.
The realtime database is very fast and ready to be used for realtime features. You push a change from one client, and any other client that is connected and watching will receive an event to respond to.
Check out projects like Firepad which use Firebase to make code editors realtime.