I’d like to share an open-source project which implements nearly all features of the google drive realtime api. Google Drive Realtime API provides Google Docs–style instant collaboration. It lets multiple people edit the same data simultaneously.
This project was inspired by Google Wave, the server runs on vert.x. It is available on github at https://github.com/goodow/realtime-store
There is also an Objective-C client library for iOS and Mac OS X, but it is not yet fully tested, so please use at your own risk!