Telephony software

Kamailio, formerly OpenSER (and sharing some common history with SIP Express Router (SER)), is an SIP server licensed under the GPL-2.0-or-later license. It can be configured to act as a SIP registrar, proxy or redirect server, and features presence support, RADIUS/syslog accounting and authorization, XML-RPC and JSON-RPC-based remote control, SQL and NoSQL backends, IMS/VoLTE extensions and others.