Asterisk

Asterisk is a free and open-source framework for building communications applications.

Asterisk is a free and open-source framework for building communications applications and is sponsored by [Digium](http://www.crunchbase.com/organization/digium). It turns an ordinary computer into a communications server. Asterisk powers IP PBX systems, VoIP gateways, and conference servers as well as is used by small businesses, large businesses, call centers, carriers, and governments worldwide.