Slack - A messaging app for teams who see through the Earth!
eXo Platform - Digital workplace solution
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
HumHub - HumHub is a free social network software and framework built to give you the tools to make teamwork easy and successful.
Cisco Jabber - Cisco Jabber lets you access presence, instant messaging (IM), voice, video, voice messaging, desktop sharing, and conferencing.
Workplace by Facebook - Connect everyone in your company and turn ideas into action.