Microsoft's virtual assistant Cortana makes her desktop debut. She's the company's answer to Siri and Google Now, and takes over the operating system's search functionality, tackling local searches as well as helping you track down stuff on the Web. The assistant can also help you stay organized: you can ask her to set a reminder, track your flights, and keep tabs on the weather.
If your Windows 10 device is equipped with a microphone, you can just say "Hey, Cortana," and she'll wait for your instructions -- you'll need to turn the functionality on. It might seem a little odd to be chatting with your PC, but if you've got something you want to remember and can't be bothered to grab a pen, it's a neat trick.
You can dictate emails to Cortana, get directions. or find cool things nearby, or simply search the Web. Ask Cortana "What do I have next week?" and she'll helpfully show you all of the events you've got lined up. On the desktop, she attempts to search for documents. Similarly, you can't manipulate calendar events or ask for directions. And many of the questions I asked Cortana on the desktop were directed to Web searches in a browser, though the phone was able to handle them just fine.
Cortana's Windows Phone presence is far more robust -- she even holds her own reasonably well against, two players in the virtual-assistant space with quite a bit more experience. But Cortana's push to the desktop is an important one, as a ubiquitous personal experience will be incredibly useful for you and everyone else. Microsoft has always pitched Cortana's chief strength as being contextually aware: if you ask her "How long will it take me to get to work," and follow up with "How long will it take me to walk," Cortana will understand that the two queries are linked and give you relevant information. The competition will treat those as two separate questions and be confused by the last one.
Cortana goes one step further: since her inception as Microsoft's virtual assistant, she's been designed with the goal of learning more, improving her capabilities as more people get on board. Relevant facts about you are stored in a "notebook" of personal preferences, which you can access (or disable) at any time. This (Microsoft hopes) will encourage people to use the virtual assistant more often, improving Cortana's accuracy and ability to parse natural language. She's also got a bit of a personality, offering witty comments or serving up a (terrible) joke -- you just have to ask.
As millions of people jump on board the Windows 10 bandwagon, Cortana will be standing by; waiting to serve, and learn -- and steadily improve. It's an ambitious goal that will require legions of Windows PC, tablet and mobile device owners to be willing to chat with their devices. But given Windows' nigh-ubiquity -- only set to grow, once it's available on devices like the Xbox One -- there's no denying that Cortana will soon be just about everywhere.