This module allows you to create your own Module using a WYSIWYG editor. The content will be shown only when your site is accessed via a given domain name/list of valid domains set in the parameters. Useful on sites with multiple parked domains. Check the right side modules, you will see that there are different instances shown depending on the domain you are on.
The Dropdown Tags Module displays all tags in the site in a dropdown menu linked to Joomla's tag specific page. You can see the demo on the right area, there are two different instances, showing the possible uses of the module.