Asterisk - An open source telephony switching and private branch exchange service for Linux.
Instadesk - Construct a "human-machine collaboration" intelligent platform to help enterprises upgrade their intelligence.
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.
Aspect Prophecy - Aspect Prophecy is a powerful, entirely standards-based platform for speech, IVR, and SIP VoIP...
FusionPBX - FusionPBX is an open source FreeSWITCH GUI.
freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).