It is a Webmin module for managing multiple virtual hosts through a single interface, like Plesk or Cpanel. It supports the creation and management of Apache virtual hosts, BIND DNS domains, MySQL databases, and mailboxes and aliases with Sendmail or Postfix. It makes use of the existing Webmin modules for these servers, and so should work with any existing system configuration, rather than needing it’s own mail server, web server and so on.
Virtualmin can also create a Webmin user for each virtual server, who is restricted to managing just his domain and its files. Webmin’s existing module access control features are used, and are set up automatically to limit the user appropriately. These server administrators can also manage the mailboxes and mail aliases in their domain, via a web interface that is part of the module.