Microsoft is currently working on its own mobile phone personal assistant, and is codenamed Cortana. Halo fans should recognize that name, as it's from one of the game's most popular characters. Like the character in the game, Cortana (the app) is built to learn and adapt to information regarding its users. According to ZDNet, Cortana manages this by using machine-learning technology and the knowledge repository (Satori) that's currently powering Bing.
ZDNet also revealed that Cortana's role in the Microsoft eco-system will be much more than just a voice activated personal assistant. According to ZDNet, there's a high chance that Microsoft will be building its "shell" which comprises services and future products like Windows Phone, Windows, and Xbox One operating systems around the unifying technology currently codenamed Cortana.
That "shell" is more than just the Metro/Modern/tiled interface. Ballmer continued: "Our UI will be deeply personalized, based on the advanced, almost magical, intelligence in our cloud that learns more and more over time about people and the world. Our shell will natively support all of our essential services, and will be great at responding seamlessly to what people ask for, and even anticipating what they need before they ask for it."
What this means that instead of just presenting simple information stored on a user's device, Cortana would need to "broker", or seek information from Microsoft's array of other services (weather, calendar, etc.). In a memo written by Microsoft's current CEO, Steve Ballmer, he claims that such a technology would enable "richer and deeper app experiences."
Unfortunately, such a technology wouldn't be available until 2014, as Microsoft is waiting for a "revolutionary instead of evolutionary" device to appear before showing the world what Cortana can do. According to The Verge, who posted some Cortana screenshots (which they reckon are stale by now), Cortana might make an appearance in the Windows Phone 8.1 update which is coming in early 2014.