When you view the source at Mudcat (or many other sites), what you see is the HTML that the server produces. That can include stuff like client side JavaScript but will not give you an idea as to how the main systems work.
The essense of Mudcat, reflected in the help forum, is a Coldfusion demo program. You can find that code here.
My own started as an asp-dev.com that I'm guessing moved onto this.
In either case,and I know for sure in my case, that it has been a case of adapting existing programs to suit needs.