Asterisk, is free, open source software that converts an ordinary computer into a feature–rich voice communications server. Asterisk makes it simple to create and deploy a wide range of telephony applications and services, including IP PBXs, VoIP gateways, call center ACDs and IVR systems.
Asterisk is released as open source under the GNU General Public License (GPL), and it is available for download free of charge. Asterisk® is the leading open source telephony project and the Asterisk community has been ranked as a key factor in the growth of VoIP.
It is used by small businesses, large businesses, call centers, carriers and governments worldwide. Asterisk is sponsored by Digium.