The Cortana iOS and Android apps launched in the US and China exactly one year ago, but the UK version features a new simplified look and feel for the apps.
The idea of the app is to extend the use of Cortana from Windows 10 PCs to smartphones, and as Microsoft has massively scaled back its plans to make smartphones running Windows Phone, that means trying to persuade iOS and Android users to get on board. Both those operating systems already have their own voice-powered digital assistants.
Users of the Cortana app can, for example, set a reminder on their PC and get it on their mobile phone, or receive missed call alerts on a Windows 10 PC and get Cortana send a text back letting the caller know you'll call them later.
Cortana can also be used to search for information, for example, with the Android app open saying 'Hey Cortana' allows you to ask questions. This feature won't be available in the iOS version.
Microsoft said the Cortana Android app is available now, with the iOS app landing in the App Store "in a few weeks".