AstraChat is an enterprise chat and messaging product that provides privacy and security out of the box.
mIRC - mIRC: Internet Relay Chat client
Mattermost - Mattermost is an open source alternative to Slack.
HexChat - HexChat is a fork of XChat with bug fixes and new features.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
irssi - Irssi is a terminal based IRC client for UNIX systems.
Slack - A messaging app for teams who see through the Earth!