FusionPBX
FusionPBX is a free and open source graphical user interface for FreeSWITCH. It can be used as a high-availability single or domain-based multi-tenant PBX, carrier-grade switch, call center server, fax server, voice-over-IP server, voicemail server, conference server, voice application server, appliance framework and more. The source code of FusionPBX is available under the MPL 1.1 software license.