/ Real Time Editing
 Collaborate - Real-time co-authoring
Enables Real-Time Collaberation Editing
Simultaneously edit a document with other authors
share your document and work together



Word PowerPoint
SharePoint ʡ .



Word 2013, Word 2016, and Word Online
2016 Live



You can simultaneously edit a document with other authors in all 3. But Word 2013 wont be as real-time as the others. The co-authoring notifications are useful but slightly less informative, edits lag a bit behind, and the number of authors editing is buried in the lower left of the status bar; no share button.
Word Online is great for general editing, and its great for real-time collaboration, but it doesnt have advanced formatting features that you might need for more sophisticated document composition. If you have to choose between Word 2013 and Word Online for co-authoring, you might lean toward Word Online if you can forego fancy stuff like fiddling with the TOC and advanced table layouts.
Word 2016 has the ideal tools for co-authoring, with the share button in the upper right, the share panel giving easy access to co-authors and real-time editing, all in the full-featured version of the software.