Cortana, for those who don't know, appeared in the game Halo.
From a report by Reuters:
Microsoft has been running its ?personal assistant? Cortana on its Windows phones for a year, and putting the new version on the desktop with the arrival of Windows 10 this fall (from the Northern Hemisphere). Later, Cortana will be made available as a separate app, usable on Apple iOS and Android phones and tablets from Google, people familiar with the project said.
There is no forecast yet for this launch and everything is still a mere rumor, but it will be very interesting if it does happen. Google also has its Now on iOS, through the central Google app. (The Verge)