Open Source Private Branch Exchange (PBX)

 Asterisk is an Open Source PBX and telephony toolkit.
 It is, in a sense, middleware
 between Internet and telephony channels on the bottom,
 and Internet and telephony applications at the top.
 .
 Asterisk can be used with Voice over IP standards
 (SIP, H.323, IAX and more),
 or the Public Switched Telephone Network (PSTN)
 through supported hardware.
 .
 Supported hardware:
 .
  * All Wildcard (tm) ISDN PRI cards from Digium
  * HFC-S/HFC-4S-based ISDN BRI cards
    (Junghanns.NET, beroNet, Digium etc.)
  * All TDM (FXO/FXS) cards from Digium
  * Various clones of Digium cards such as those by OpenVox
  * Xorcom Astribank USB telephony adapter
  * Voicetronix OpenPCI, OpenLine and OpenSwitch cards
  * CAPI-compatible ISDN cards
    (using the add-on package chan-capi)
  * Full Duplex Sound Card (ALSA or OSS) supported by Linux
  * Tormenta T1/E1 card
  * QuickNet Internet PhoneJack and LineJack
 .
 This is the main package
 that includes the Asterisk daemon
 and most channel drivers and applications.