script installers

is there any information anywhere on how to build our own script installers? with the GPL version, there is a few different applications (phpmyadmin, WHMCS, etc) which can be auto-installed by users.

I realize that with a licence you get a large amount of these script installer packages, and thats great. but i'd like to build my own out of a few key targets, such as wordpress, joomla, and a few others.

i'm sure its not all the difficult, and if i have to i can dig into the source for virtualmin, or in the packages, and take a peek at how its done

but id like to know

a) if there is any existing information on how to do so out there

and b) is there any mechanism stopping us from doing this without a licence?

thank you!