Asterisk - An open source telephony switching and private branch exchange service for Linux.
Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
FusionPBX - FusionPBX is an open source FreeSWITCH GUI.
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).
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.
Lingo - Empower Creation and Ensure Brand Consistency. Build and Share libraries of visual assets with your entire team — all from your desktop.