freepbx - FreePBX is a web-based open source GUI that controls and manages Asterisk (PBX).
Avaya Voice Portal - Voice Portal delivers on industry leading IT fit, reliability, scalability and manageability.
Asterisk - An open source telephony switching and private branch exchange service for Linux.
Scorebuddy - SO WHAT IS SCOREBUDDY ALL ABOUT? Years ago, physical score cards or computer spreadsheets were used to track customer interactions.
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.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.