The FreePBX Distro is an open source unified communications software system that consists of a graphical user interface (GUI) for configuring, controlling, and managing Asterisk PBX software. The FreePBX Distro includes packages that offer VoIP, PBX, Fax, voice-mail and email functions. FreePBX is licensed under the GNU General Public License (GPL).The FreePBX Distro Linux distribution is based on CentOS, which maintains binary compatibility with Red Hat Enterprise Linux.