Asterisk, The Open Source PBX
Asterisk is an open source PBX and telephony development platform. Asterisk
can both replace a conventional PBX and act as a platform for the
development of custom telephony applications for the delivery of dynamic
content over a telephone; similar to how one can deliver dynamic content
through a web browser using CGI and a web server.
Asterisk supports a variety of telephony hardware including BRI, PRI, POTS,
and IP telephony clients using the Inter-Asterisk eXchange (IAX) protocol (e.g.
gnophone or miniphone). For more information and a current list of supported
hardware, see http://www.asterisk.org