Asterisk is an open source telephony engine. In 1999, Computer Engineer Mark Spencer was running a tech support business and he wanted a way to distribute calls to his employees, but didn’t want to purchase an expensive PBX. Instead, he began work on a program that would do it for him. This became Asterisk. Asterisk variations are now available on Windows, Mac, and Linux operating systems, and it is the basis for many open source and propriety PBX and hybrid PBX systems.

Open Source software means the code is available to any developer to build on and modify, so long as that modification is available to anyone. Through this process, the untold number of professional programmers and hobbyists find and fix bugs, and come up with new innovations. The opposite of this is “closed source” or “proprietary” software, where one company develops in-house or with carefully selected partners. For example, Google’s Android is open source, and Apple’s iPhone is not. Many different companies have released their “flavor” of Android phone, which can be in any shape or size. In contrast, there is only one iPhone.

Asterisk can run on any regular computer, but it is often integrated into dedicated hardware. Most programmers run Asterisk on Linux because Linux is lightweight and free to use. But, it works well on any operating system, including emulated software. The more you need Asterisk to do, the more computing power you’ll need. An Asterisk-based system also needs a gateway in order to connect to the PSTN. Again, the more you want your system to do, the more computing power you’ll need. Even though the Asterisk engine is free, the hardware you’ll need to run it at a professional level can be many thousands of dollars.

Asterisk is a “blank slate.” To configure an Asterisk system, a programmer must configure a number of rules regarding the flow of information. This is good, because a skilled engineer can make a completely customized business solution, covering everything from telephone numbers to phone trees to an online portal. But, in order to do all that, you have to be a skilled programmer who can properly understand coding. This is why many companies build on top of Asterisk, and sell that service as a “PBX in a box.”

There are many variations, both free and commercial, of Asterisk. Fonality developed a version with many add-ons and a graphic user interface that they called “Asterisk@Home,”and later renamed “trixbox.” trixbox is available as a “CE” community version, which is open source, or as a commercial “Pro” version. trixbox CE is the most popular Asterisk variation, and it has been downloaded over two million times.