Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
Crypho - End-to-end-encrypted messaging and file sharing
Keybase Chat - End-to-end encrypted chat built into Keybase
MushRoom - KnockKnock the person whom you want to message and he/she should accept your knockRoom or Group can be created by providing a nameShare Room link with your friends to join the conversationWatch video or listen music during conversation
Signal - Fast, simple & secure messaging. Privacy that fits in your pocket.
dPhone - The most secure calling app. Open Source and Free.