FreePBX

FreePBX is a free, open-source graphical user interface (GUI) that controls and manages Asterisk, the most widely deployed open-source PBX engine. It provides a web-based admin panel for configuring extensions, ring groups, IVR menus, voicemail, and more.

Many VoIP service providers use FreePBX (or its commercial distribution, Sangoma PBXact) as their PBX backend. When paired with a white-label softphone front-end, providers can offer a complete hosted telephony solution under their own brand.