Asterisk is open-source PBX software and a telephony toolkit. It sets up and controls calls between phones, the public telephone network and VoIP devices, and offers features found in commercial PBXs such as voicemail, conferencing, interactive voice response (IVR) menus and automatic call distribution. It supports SIP, H.323 and its native IAX protocol, among others, and can be extended with dial plan scripts, modules and AGI programs. Asterisk is written in C, runs mainly on Linux, and is installed and operated by the organisation itself. The project does not provide a hosted service of its own.
Asterisk was created in 1999 by Mark Spencer of Digium in Huntsville, Alabama (USA). Since 2018 Digium has been part of the Canadian company Sangoma Technologies Corporation of Markham, Ontario, which holds the copyright and trademark and is the main developer and sponsor. The code is licensed under GPLv2, with additional licences available from Digium. Because you run Asterisk on your own infrastructure, you decide where call data and logs are stored, for example within the EU.