The best open source alternative to FreePBX is Asterisk. If that doesn't suit you, our users have ranked more than 25 alternatives to FreePBX and nine of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to FreePBX are FreeSWITCH, Yate - Yet Another Telephony Engine, Wazo and FusionPBX.
Asterisk is an open source framework for building communications applications. Asterisk turns an ordinary computer into a communications server. Asterisk powers IP PBX systems, VoIP gateways, conference servers and other custom solutions.
FreeSWITCH is a scalable open source cross-platform telephony platform designed to route and interconnect popular communication protocols using audio, video, text or any other form of media. It was created in 2006 to fill the void left by proprietary commercial solutions.
Yate is a softswitch (concept of separating the network hardware from network software).
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...
FusionPBX is an open source FreeSWITCH GUI. FusionPBX can be used as a high available single or domain based multi-tenant PBX, carrier grade switch, call center server, fax server, voip server, voicemail server, conference server, voice application server, appliance framework...
Kamailio® (successor of former OpenSER and SER) is an open source SIP server released under GPL, able to handle thousands of call setups per second. Among features: asynchronous TCP, UDP and SCTP, secure communication via TLS for VoIP (voice, video); WebSocket support for...
IvozProvider supports multiple management levels, from Global platform administrator to final user, each of them having its own web interface with visibility to perform configuration tasks.
OpenSIPS (Open SIP Server) is a mature Open Source implementation of a SIP server. OpenSIPS is more than a SIP proxy/router as it includes application-level functionalities. OpenSIPS, as a SIP server, is the core component of any SIP-based VoIP solution.
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FreePBX is a full turn key PBX with GUI. Freeswitch is just the switch and is more similar to Asterisk (what FreePBX runs on under the GUI).