Are there any 1 click install scripts for things like wordpress, drupal, etc to offer to customers?
yes it comes with virtualmin pro. it is not 1 click, there are 3 clicks though
what ones does it offer?
are you not allowed to have reseller plans on GPL?
You can see the full list of available Install Scripts here:
The GPL version of Virtualmin does not have the Reseller feature -- you can see a list of differences from the GPL version to the Pro here:
Joomla! is missing in the full list of scripts..