Asterisk

Asterisk is an open‑source IP PBX, VoIP gateway and conference server that acts as middleware between Internet‑based telephony channels and traditional PSTN interfaces. It supports SIP and other VoIP protocols while also handling analog and digital hardware such as Sangoma interface cards, PortAudio sound cards and Xorcom channel banks, allowing integration of both modern and legacy telephone systems.

The software is self‑hostable, free‑tier and does not require a subscription, and is released under the GPL‑2.0 license. It runs primarily on GNU/Linux distributions but has been reported to work on macOS and BSD variants, with installation requiring a C99‑compatible compiler, standard development libraries and optional modules selected via `make menuselect`.

Asterisk is intended for organizations and developers who need a configurable telephony platform for routing calls, managing extensions, and hosting conferences. Its documentation includes security guidance, build instructions, and upgrade notes, and the project is maintained by an active community of contributors and the sponsoring company Sangoma.