Cortana, Microsoft’s clever digital assistant on Windows Phone 8.1, makes the jump to PCs with Windows 10, where she assumes control of the operating system’s search functions. Cortana will want to access your personal info, then use that info along with her Bing-powered cloud smarts to intelligently surface information you’re looking and perform other helpful tasks.
Cortana can help you find all sorts of online information via natural language queries you ask using text or voice commands. Cortana can also apply those natural language smarts to use search your hard drive, OneDrive, and business network for files that meet certain filters, like “Find me pictures from May.”
It’s deeply cool… though the initial Cortana build can be a bit flaky. She's a lot smarter (and funnier) in Windows Phone 8.1; the Windows 10 version just needs a bit more time in the oven.