Google Drive release the real-time API
Developing for the Drive Realtime API is almost as simple as working with local objects. The API provides collaborative versions of familiar data objects such as maps, lists, strings, and JSON values and automatically synchronizes and stores modifications to these objects. Your application reads from and writes to these objects like any other local object. Change event handlers can be added to collaborative objects so that your app can react to changes from other collaborators.
Because the Drive Realtime API is based on operational transformation (OT), local changes are reflected instantly, even on high-latency networks. The Drive Realtime API automatically transforms changes to the data model so that every collaborator stays in sync.
If basic collections aren’t enough for your application, the Drive Realtime API supports custom objects and references, including trees and arbitrary graph structures. As with other collaborative objects, the Drive Realtime API automatically synchronizes these objects with other collaborators and stores them in Drive.
Because presence is important in collaborative applications, the Drive Realtime API also keeps track of who is connected to your application and provides your app with events for when collaborators join, leave, or make changes.