RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies
Asterisk - An open source telephony switching and private branch exchange service for Linux.
MightyCall - Virtual phone system that lets you run your business from anywhere.
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.
JustCall - The Cloud Phone System of choice for modern sales and support teams. We help end clueless conversations by adding context to every call.
FusionPBX - FusionPBX is an open source FreeSWITCH GUI.