Microsoft today announced new capabilities of Office Online that show the company being more open to editing files stored in other cloud file storage systems.

Now Office Online offers real-time coauthoring — allowing multiple people to work on documents and see each other’s activity at the same time — for documents living inside Box, Dropbox, Egnyte, and Citrix ShareFile, Microsoft Office corporate vice president Kirk Koenigsbauer wrote in a blog post. The companies are part of the Cloud Storage Partner Program (CSPP) that Microsoft introduced last year.

Dropbox Basic, Dropbox Pro, and Dropbox Business users with paid Microsoft Office 365 licenses can all use this new feature now, Michael Shaffer, Dropbox’s vice president of business development and partnerships, wrote in another blog post.

The agnosticism of where files are actually kept — and support for on-premises storage by way of Egnyte and Citrix ShareFile — could make Office Online a stronger challenger to Google Docs.

Microsoft is also allowing companies in the CSPP to integrate their files with Office for iOS, such that Office for iOS users can open and edit files from other clouds within the app. This feature is actually already live for Box. You can even “create a fresh Word, PowerPoint, or Excel document, assign tasks to specific colleagues and save to Box,” Box associate product manager Edward Shi wrote in his own blog post.

Microsoft is also broadening the capability of sharing files from third-party cloud storage services on Outlook.com. People using the site will be able to attach Dropbox, Box, and OneDrive files as documents or links “in the coming weeks,” Koenigsbauer wrote.

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