TeamViewer - TeamViewer lets you establish a connection to any PC or server within just a few seconds.
Asterisk - An open source telephony switching and private branch exchange service for Linux.
AnyDesk - AnyDesk is the world's most comfortable remote desktop application. Access all your programs, documents and files from anywhere, without having to entrust your data to a cloud service.
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.
ConnectWise Control - ConnectWise Control is a mobile app that allows you to instantly connect with another system from anywhere with a connection to the internet. The software not only comes in a mobile app, but it has a desktop version as well for complete coverage.
freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).