Cortana is a digital assistant from Microsoft for Windows Phone OS, it is similar to the Google Now and Siri on iPhone. Microsoft promised that it will be available on rival platforms iOS and Android. An Android version of the Cortana is made available few months back for testers, now iOS testers also got the taste of Cortana on their i devices.
A few selected testers were notified of the early version of Cortana by way of email according to reports. Cortana offers assistance recognizing natural voice, it can help you track packages, answer questions using information from Bing like weather, traffic conditions, sports scores and of course it can give funny answers as well. Currently it is only available to handful of testers who have singed up for the program. When it is ready for the prime time then it will be available to all of you through App store, till then Microsoft would add features and fix bugs if any. But there is no time frame or schedule for when it will be made available on the app store for public.