Powered by Bing, Cortana is an intelligent personal assistant in the same vein of Apple’s Siri and Google Now. But unlike Siri, there are APIs, so third-party app integration is possible. Cortana is activated by either a Live Tile on the Start screen, or by a press of the Search button. You can speak to it, or input text to issue commands. Like a real human assistant, it stores what it knows about you in a ‘notebook’, which you can easily revoke access to. When Cortana is launched (as a beta) in Windows Phone 8.1 this year, only a few regions will get it: the U.S., the U.K., and China. For us in Asia Pacific, we’ll have to wait till 2015 (or you could just change the region setting).
The effectiveness of Cortana increases over time as it gathers more information about you.