Asterisk

Asterisk is the widely used open-source communications framework, originally created by Mark Spencer at Digium and now maintained under Sangoma Technologies following its acquisition of Digium in 2018. It provides the core software for building private branch exchange systems, voice over IP gateways, conference servers, interactive voice response applications and other real-time communications solutions. Organisations and service providers have long needed a flexible alternative to proprietary telephony hardware, which tends to be expensive and difficult to customise. Asterisk addresses this by turning standard servers into full-featured telephony platforms, supporting SIP trunking and a wide variety of protocols, codecs and telephony interfaces. Its approach favours extensibility: developers and integrators can script call flows, add modules and connect Asterisk to databases and business systems, which has made it a foundation for countless commercial products and custom deployments worldwide.

Asterisk provides capabilities including call routing, voicemail, conferencing, call queues, call recording, music on hold, interactive voice response and support for analogue and digital telephony cards alongside VoIP endpoints. Programmatic interfaces such as the Asterisk Manager Interface and the Asterisk REST Interface allow external applications to control calls and build advanced services. Although the core is free and open source, Sangoma supplies commercial offerings around it, including FreePBX and PBXact, which add graphical administration, commercial modules, phones, gateways, SIP trunking and professional support, as well as cloud-hosted and on-premise business phone systems. This ecosystem allows organisations to choose between self-managed deployments and supported solutions. Asterisk is used by telecommunications carriers, internet telephony service providers, contact centres, systems integrators, universities and enterprises that need a highly customisable communications platform. A free version is available through the open-source project, a free trial is offered for commercial products, and paid options start from around USD 595, typically for hardware, licences or support packages.