FreePBX
FreePBX is a web-based open source GUI (graphical user interface) that controls and manages Asterisk® (PBX), an open source voice over IP server. FreePBX is licensed under the GNU General Public License, an open source license. FreePBX can be installed manually or as part of a pre-configured FreePBX Distro that includes the system OS, Asterisk, FreePBX GUI and assorted dependencies.