Q: I'm trying to offer free hosting and don't know of any way to allow the public to create their own accounts from a form. Can you tell me if there is any available scripts or programs for this?

A: You can use Plesk Command Line Interface to perform Plesk operations in your scripts. You can find corresponding documentation here. Please note that CGI scripts are run as domain ('FTP') user. You can use various wrappers to run Plesk Command Line Interface as root with secure way.