The new head of the world's biggest software company took the stage nearly three hours into a marathon keynote. It "began" with a new version of Windows Phone -- that adds an instant Skype button, like Apple's Facetime -- and predictive alerts like Google Now.
"We think when a phone knows you, you have a better experience with it," Nadella said.
There's a speedy new keyboard. But Windows Phone still lags behind the others in apps. Microsoft wants to change that:
"It's my pleasure to introduce universal windows apps," Nadella said.
Just like it sounds, developers can build one app that'll adjust itself to run on your phone, tablet, soon, even your Xbox -- and even your desktop PC.
Speaking of those -- they're finally fixing Windows 8:
"Run your windows applications with the new start menu," Nadella said.
It's hardly new. The start menu's been around for almost 20 years, but Microsoft removed it in Windows 8 -- and users revolted. Now, they're back-tracking to make the new touchable Windows a little better for the old keyboard and mouse. If you have Windows 8.1, the update is free.
But the announcement likely to be the most talked about is one that's doing quite a bit of talking itself. or more accurately, herself.
True geeks know Cortana's named after a character in the "Halo" video games. Just like her namesake, she's artificially intelligent.
"I'll add dentist appointment to your calendar," she says during the presentation. "Just so you know -- you have to pick up Christina from airport at the same time."
And unlike Apple's "Siri," -- Cortana is open to app developers. So you could add shows to queues in Hulu, for example, with a voice command. Thousands of developers at the Build Conference will likely teach Cortana new tricks.
The Windows Phone update will roll out "slowly' -- over the next few months.