Since 2013, we’ve offered real-time co-authoring with Office Online documents stored in Microsoft OneDrive and SharePoint Online. Today, we are extending this capability to cloud storage providers in the CSPP program. Real-time co-authoring with Office Online is now available for users whose documents are stored in Box, Citrix ShareFile, Dropbox and Egnyte. Also starting today, any other partner in the CSPP program can enable real-time co-authoring using standard interfaces. Microsoft Extends Real-Time Authoring Of Office Online To Cloud Provid [blogs.office.com]

in addition to Dropbox, we’re offering all CSPP partners the opportunity to tightly integrate with Office for iOS.