Microsoft CEO Satya Nadella at Microsoft Build 2015 Microsoft Today, Microsoft officially released the Microsoft Graph, a nerdy solution that opens the doors wide for developers to do a lot more with Microsoft Office.

The critical idea here is the "application programming interface," or API. Programs use APIs to talk to each other — popular fitness app Runtastic, for example, uses the Google Maps API to display a real-time map on the app.

The Microsoft Graph, first announced in beta back in April, is a set of APIs that blow open the Microsoft Office 365 productivity cloud to developers, letting them build apps that take a user's data and put it to use in cool, new ways.

Basically, it means that any developer can build an app that taps straight into the data that lives inside Office 365, making their wares smarter and faster.

"It's not just all about Microsoft," says Rob Lefferts, Microsoft general manager of Office exentensibility. "It's a huge starting set of information."

And just like Facebook's famous social graph, the Microsoft Graph lets developers ask questions of the data like, "Who does my customer work closely with?" The intelligence is handled by Microsoft on the back end. (And no, it's not as creepy as it might sound — like any other app, you'd have to give it permission to access data.)

For instance, Lefferts says, over 850 million meetings per month get booked via Microsoft Outlook for Office 365. That means that there's tons of data there for an enterprising app developer to build a predictive calendar based on how users spend their time.

At launch, the Microsoft Graph supports data from sources like e-mail, the address book, and calendars. Later, it'll be able to support data taken from OneDrive storage, OneNote cloud notes, and other Microsoft data.

The Office Graph also goes both ways. For example, security startup Skyhigh Networks is already using the Microsoft Graph to enforce enterprise policies on customers' Office 365 installations, scanning and quarantining files that live in the cloud.

For developers, the first taste of Microsoft Graph is free, Lefferts says. But if they're using Microsoft Office data at volume in their own apps via Microsoft Graph, the company will collect a fee.

It will be a while before most developers figure out how to best access all that data, since the Microsoft Graph is new.

But it has the potential to make apps much smarter, in a behind-the-scenes kind of way. And it's good for Microsoft, because it means that customers can get more out of the money they're sinking into Office 365.

"The demand of customers is to say, 'make it seamless, make it great," says Lefferts.