There's also DeltaChat: It looks more or less like WhatsApp, but it uses email as the transport and storage mechanisms, and it is seamlessly encrypted with Auto

There's also DeltaChat: It looks more or less like WhatsApp, but it uses email as the transport and storage mechanisms, and it is seamlessly encrypted with AutoCrypt. It supports both one-on-one and group chats. It has apps for mobile and desktop. ⌘ https://delta.chat/ https://delta.chat/