Virtualmin is a virtual hosting management system written by Jamie Cameron, that integrates cleanly into the Webmin system administration tool.

What does it do?
Currently, Virtualmin is a two-tiered virtual hosting administration system (a third tier for individual users is provided by Usermin). It has good support for disk quotas, user-based POP3/IMAP email setup (rather than Cyrus or other "virtual" types of mailbox methods--this was by design, though there is nothing to prevent other types of mail user from being supported in the future if there is incentive), Apache virtual host entries, BIND domain setup, Postfix and Sendmail email address and alias management, and MySQL database creation. The second tier, used by the domain owner, allows for creation of email accounts and aliases within the domain, as well as Apache virtual host details, BIND domain details, and access to the domains MySQL database.