Seald - Keep your conversations secure, everywhere.
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
Keybase Chat - End-to-end encrypted chat built into Keybase
Brie.fi/ng - Start secure group video chat
Spike - Spike solves businesses' communication chaos by bringing together email, team chat, collaborative docs, and meetings, into one feed.
Slack - A messaging app for teams who see through the Earth!