Asterisk - An open source telephony switching and private branch exchange service for Linux.
Invoca - Call tracking & analytics software
Wazo.io - The UCaaS Platform Built for MSPs
CallTrackingMetrics - Know who is calling and how they found you. Maximize the return on your advertising.
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.
Marchex - Marchex is a mobile advertising analytics company that connects online behavior to real-world, offline actions.