Empathy - Apps/Empathy - GNOME Wiki!

Everleagues - Everleagues is a cloud-based application that offers team communication, file sharing and storage, data tracking, and activities management.

Pidgin - Pidgin is an easy to use and free chat client used by millions. Connect to AIM, MSN, Yahoo, and more chat networks all at once.

openmeet - Account free video conferencing with a rooms component that lets you use VC within a physical meeting room. The server can also be hosted in your own cloud for extra privacy/security.

Trillian - Trillian is a decentralized and federated instant messaging platform that lets your whole company send private and group messages, keep tabs on what co-workers are doing, share files, and much more.

Stork.ai - AI-Based Collaboration for Hybrid Teams. Rich media messaging, advanced video and voice conferencing, auto-transcribing and screen sharing. Serendipitous meetings at the water-cooler with your human and AI teammates.