What are some alternatives?
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
Zulip - Powerful open source group chat
MyChat - Secure instant messenger for any network
Sesame Chat - A Self-Aware, Digital Assistant that Protects Your Messages
MagicPad - Free, simple, and private, offline text encryption suite.
WhatsApp - WhatsApp Messenger: More than 1 billion people in over 180 countries use WhatsApp to stay in touch with friends and family, anytime and anywhere.