freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).
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.
FreeSWITCH - FreeSWITCH is an open-source media application designed to support popular protools such as SIP and WebRTC and provides a platform to develop voice and video applications.
WebEx - Cisco WebEx Web Conferencing, Online Meetings, Desktop Sharing, Video Conferencing
Asterisk - An open source telephony switching and private branch exchange service for Linux.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.