Empathy - Apps/Empathy - GNOME Wiki!
Zoom - Equip your team with tools designed to collaborate, connect, and engage with teammates and customers, no matter where you’re located, all in one platform.
Gajim - Full featured and easy to use Jabber client
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Psi-IM - Psi-IM is a messaging program that is designed for the XMPP network.
WebEx - Cisco WebEx Web Conferencing, Online Meetings, Desktop Sharing, Video Conferencing