iOS 15's FaceTime now allows its users to call people using an Android device or Windows PC. As per CNBC, previously FaceTime is only exclusive to Apple users with an iPhone, iPad, and even Macs. However, for the first time, through the iOS 15 update, FaceTime is now also available on Android and Windows users, at least via browser.

Link: How to FaceTime Friends With Android Device or Windows PC in iOS 15
via http://www.techtimes.com