Real time co-authoring allows multiple people to edit a document in Office 365 at the same time.
Microsoft has supported storing files in DropBox, Box and other cloud storage services and loading them into Office Online directly from these services. However, real time co-authoring was not supported.
This has now changed and real-time co-authoring support is now provided for DropBox and BOX with other cloud storage partners expected to provide support for it soon.
