Dialpad - Switch is a cloud-based phone system built for Google Apps users.
freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).
GlobalMeet Collaboration - From cloud PBX to conference calls and meetings to online events, GlobalMeet is a business communications platform that helps take you where you need to go.
Asterisk - An open source telephony switching and private branch exchange service for Linux.
MiCloud Connect - Secure and flexible cloud phone services and unified communications.
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.