Asterisk is telephone private branch exchange (PBX) software which allows telephones of a private network to call each other and also caters connections to public switched telephone network (PSTN) and Voice over Internet Protocol (VoIP) services.  AsteriskNOW includes Asterisk, the AsteriskGUI, Digium/Asterisk Hardware Device Interface (DAHDI) driver framework, FreePBX GUI and softwares for an Asterisk system.