The FreePBX Distro is a freeware 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, IVR, voice-mail and email functions. The FreePBX Distro Linux distribution is based on CentOS, which maintains binary compatibility with Red Hat Enterprise Linux. FreePBX has contributed to the popularity of Asterisk.