Facebook Messenger

 Whatever your take on the social network of record, its messaging app is without equal. You don't need a phone number to use Facebook Messenger, and you can use it on any device without the need for your phone to be present as it must with WhatsApp.

It works on every platform, unlike iMessage. It also has many cool features, like audio calling and video chatting with AR masks, stickers, and mobile payments. You can even play games through it with your contacts. Oh, and all of that's free.