In the Excel Web App, for example, multiple users can open a workbook from either Windows Live SkyDrive or SharePoint 2010 and make changes that appear in near real-time, allowing you to see each other’s edits as you work. And as people make changes, the charts, conditional formatting, Sparklines and other data-driven functions will update as well.
To see who else is editing a file in Excel, you’ll notice a pop-up in the status bar (bottom-right) which shows you who is editing along with you.
The OneNote Web App also allows for co-authoring of the same shared notebook with others who have opened the file as a Web App, or, in this case, even those who are using the desktop software OneNote 2010 and its “shared notebooks” feature. Again, changes sync in near real-time, just as with Excel.
You can also see who has made what edits specifically by clicking “Show Authors” on the Ribbon’s “View” tab. From this tab, you can see previous versions of a page by clicking “Page Versions.” You can restore or delete previous versions, too, if desired.
Right now, co-authoring is supported in the Word, PowerPoint and (via shared notebooks) the OneNote desktop applications when a file is opened from SkyDrive or SharePoint 2010. Co-authoring will arrive for all Web Apps by the second half of this year.