The Incredible PBX!

Wazo is mainly an IPBX that provides communication services such audio, video, and instant messaging based on the use of standard network technologies such as the TCP/IP protocol. It is interoperable with most market telephony systems and gives users access to flexible and advanced services without requiring specialized hardware.

XiVO is a scalable platform based on Asterisk that offers a free and complete PBX solution. It is licensed under the GPLv3.

Elastix is an open source Unified Communications Server software that brings together IP PBX, email, IM, faxing and collaboration functionality. It has a web interface and includes capabilities such as a Call Center software with predictive dialing.

AsteriskNOW is the fastest way to get started building custom telephony solutions with Asterisk. Simply download the .iso file, burn it to a CD, drop it into the CD or DVD drive on the target computer and in less than 30 minutes you will have a full functional Asterisk system ready for your custom telephony application.

PBX in a Flash is a PBX system based on Asterisk, FreePBX and CentOS, coming as an ISO download. A two stage installation process allows for more flexibility for the installation of the PBX specific components. The Asterisk components are compiled from source during the install process which allows for easier adaptions later on. The system is update-able without re-install. A script collection on pbxinaflash.org allows for easy extension of the base system.

Ombutel is a joint venture of Telesoft and Xorcom that offers a free phone system based on the solid Linux and Asterisk platforms, offering whole new level of user experience with offers fully-responsive user interface that looks great, and is easy to use, on any screen size. Ombutel utilizes the latest technologies in Linux and Asterisk to provide a highly secure system on all levels.

FreeSentral is a full IP PBX consisting of a Linux Distribution, an IP PBX and a Web Graphical User Interface for easy configuration

The Taridium ipbx is a complete software-based VoIP PBX system that replaces traditional proprietary hardware PBX. ipbx runs on an open source operating system (Linux) without the need for extra software licenses and is based on the SIP standard. Choose from many SIP based hardware phones such as Aastra, Cisco, Polycom or Linksys, instead of getting locked in with one vendor.