Cruise the hallways of Microsoft's Redmond campus, peer into doorways, and observe what kinds of collaborative apps are running on the multiple monitors attached to every PC.
Here are some you won't often see: Yammer, SharePoint, Skype, and the Web versions of Word, Excel, Outlook, and PowerPoint. On a developer's machine you'll always see Visual Studio. On a product or program manager's machine you might see Word, Excel, or PowerPoint.
But there's one app you'll always see. It dominates all others, it runs everywhere, it's the first app you install on a fresh PC, and it's the one you'll call support in the middle of the night to fix. It's deeply wired into the company's DNA, and it remains, as it has always been, the bedrock of online collaboration at Microsoft.