Asterisk - An open source telephony switching and private branch exchange service for Linux.
KOOKOO - All in one solution for calls, IVR, live chat, customer management & more.
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.
Dialfire - Cloud Calling at Jet Speed
FusionPBX - FusionPBX is an open source FreeSWITCH GUI.
Aircall - Aircall is a call center software of a new generation designed for fast growing companies. Setup instantly and integrates to your CRMs