Wikipedia
FreePBX
FreePBX is a web-based open source GUI ( graphical user interface) that controls and manages Asterisk (PBX), a voice over IP server.
FreePBX is licensed under the GNU General Public License and is a component of the FreePBX Distro (independently maintained Linux system derived from the source code for the CentOS distribution with the PBX pre-installed); it is also included as a key piece of various third-party distributions like The FreePBX Distro and AsteriskNow.
FreePBX was taken over by Schmooze.com in early 2013; that firm was in turn taken over by Sangoma Technologies Corporation on Jan 2, 2015.