The Windows Phone personal assistant will soon be available to download on its biggest rivals' handsets.
Just like Android's Google Now and Apple's Siri, Cortana is a digital personal assistant who can respond to voice commands and queries and help you keep on top of your appointments schedule. Users will also be able to sync Cortana on their handset with the personal assistant on their Windows PC.
When running on a Windows Phone, the service offers even more, but how it performs on the iPhone or a Nexus device will be limited by the fact that it won't have the same levels of access to a handset. Just how much won't be clear until it launches on Android at the end of June and for Apple devices some time later.