What are some alternatives?
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
1ty.me - If you need to send a password or some other form of simple but sensitive information to someone...
MyChat - Secure instant messenger for any network
SafeNote - Encrypt and send files and notes with a link that automatically destruct after being read to ensure your important documents don’t stay online forever.
MagicPad - Free, simple, and private, offline text encryption suite.
Slack - A messaging app for teams who see through the Earth!