Multiple authors can work simultaneously in PowerPoint for the web and PowerPoint 2016. Real-time presence helps you see where your co-authors are working in the presentation so that you don't create conflicts as you edit, and you can see changes as they're being made. PowerPoint 2013 supports simultaneous editing, but there is no presence indication, and changes can't be seen by multiple authors until the document is saved. For more information about real-time co-authoring in PowerPoint, see Work together on PowerPoint presentations.