The software in use falls naturally into several major classes, each of which contain sub-classes.
Software which I have written is generally in the Perl programming language and is released under the 2-clause BSD license, which essentially means that you can do pretty much whatever you want with it as long as you give me credit for the original work and understand that there is no warranty protection. If it breaks, or if it breaks your system, you get to keep the pieces at no additional charge.
Perl is often, and unfairly, described as a write-only language. My scripts generally contain a plethora of commentary material which explains how and why particular activities are taking place.