Cortana is not the code name of a new operating system from Microsoft; it is the name of an AI character in the Halo games, and also of a possible future competitor for Apple's Siri, but on Windows mobile devices and perhaps computers. Part of the power behind what could be a rather sophisticated "personal assistant" is Bing's Satori technology.
Cortana will be more than just an app that lets users interact with their phones more naturally using voice commands. Cortana is core to the makeover of the entire "shell" -- the core services and experience -- of the future versions of Windows Phone, Windows and the Xbox One operating systems, from what I've heard from my contacts.
In Microsoft CEO Steve Ballmer's strategy memo from July about Microsoft's reorg, there were hints about Cortana. Ballmer mentioned that Microsoft will be working, going forward, on "a family of devices powered by a service-enabled shell."ZDNET
|Cortana, as seen in Halo 4|