The -- though not officially called an "app store" due to a with -- launched in beta this month with 100 and 400 professional services from Microsoft partners. The apps and services are available for Exchange, Lync, Office and SharePoint, but SharePoint is the real key for the app store, suggests Gartner analyst Mark Gilbert.

"I've been suggesting to Microsoft that they needed an app store for SharePoint for probably five years now," he says.

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Despite the previous lack of an app store, a large number of third-party vendors have built applications to add functionality to .

But with Microsoft trying to expand usage of SharePoint Online, Gilbert says tools for customizing SharePoint and industry-specific services will be necessary. For example, HR departments or pharma companies want reliable tools that are geared toward their specific needs and help them get SharePoint deployments up and running, he says. In general, SharePoint requires more customization than other Microsoft software.