Asterisk corporate telephone switch

Alternative to: Avaya IP Office 500
Where to find it: http://www.asterisk.org/

A corporate telephone switch—known as a private branch exchange—is the piece of equipment that makes it possible to dial a colleague's extension using four or five digits. Not only does it route phone calls within the company but it also connects the corporation to the telephone network. A number of companies including Digium and Fonality offer low-cost telephone switches for businesses that are built off the Asterisk open-source software, initially developed by Mark Spencer (pictured).