Over the last couple of weeks Kontalk made it into two lists of Whatsapp alternatives:
Kontalk is an open-source, free chatting app for Android, web, and desktop. You can keep all the files entirely on your super secure server. You will be the only person in charge of all the chats you have with your friends and family
https://vpnpro.com/blog/alternatives-to-whatsapp/
We particularly like: The ultimate in privacy, the open XMPP format of this app means that you are totally in charge of your chat privacy