No special software needed. Whether you have an Android phone or a Windows PC, Apple made it so you can join FaceTime calls with iPhone owners.

Even though a Windows user can join a FaceTime call, the call has to be initiated from an Apple device. They don’t have the option to start a call from their computer, which is a little awful ...

There's one limitation, though. Android and PC users can't start a FaceTime call on their own. They'll need an Apple user to create the link and invite them before they can join in.