Empathy - Apps/Empathy - GNOME Wiki!
RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Psi-IM - Psi-IM is a messaging program that is designed for the XMPP network.
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Gajim - Full featured and easy to use Jabber client
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs