If they don’t have Whats App, you can easily send them an invite.
You can choose to either have a voice or video call, and you can also share your screen.
And if you’re worried about privacy, you can “lock” your call to prevent anyone else from joining if they somehow found your unique link.
It’s unlikely many of your contacts use the app, but if they do, it also doubles up as a messaging app, where you can record and send text messages and videos.
It’s basically like Whats App, but also allows calls to landlines and web-based calls to non-users. Also, includes games, public chats, and calls to mobiles and landlines.