Elastix is a software-based PBX powered by 3CX and based on Debian. An open-standards solution, Elastix is an easy to install and manage UC system compatible with popular IP phones, gateways and SIP trunks.
Elastix is complete with unified communications features such as integrated WebRTC video conferencing, chat, presence and softphones and smartphone clients for Windows, Mac, iOS and Android.
Asterisk is a software implementation of a private branch exchange (PBX). In conjunction with suitable telephony hardware interfaces and network applications, Asterisk is used to establish and control telephone calls between telecommunication endpoints, such as customary telephone sets, destinations on the public switched telephone network (PSTN), and devices or services on voice over Internet Protocol (VoIP) networks. Its name comes from the asterisk (*) symbol for a signal used in dual-tone multi-frequency (DTMF) dialing.
FreePBX is a web-based open-source graphical user interface (GUI) that manages Asterisk, a voice over IP and telephony server.
FreePBX is licensed under the GNU General Public License version 3. It is a component of the FreePBX Distro, which is an independently maintained Linux system derived from the source code of the CentOS distribution, having Asterisk pre-installed. It is also included in various third-party distributions such as The FreePBX Distro and AsteriskNow.