Webmin is a free server administration interface for Unix-like systems. It allows the users to internally configure the operating systems and modify open-source apps like Apache HTTP Server, PHP, MySQL etc. It allows you to setup user accounts, Apache, DNS, file sharing and much more using any modern web browser. Users can manage the system remotely or from the console and it provides you the comfort to get rid of manual editing of Unix configurations like passwords. The web server and CGI programs of Webmin are written using standard perl modules.
To extend the functionality of Webmin, custom modules can be inserted. There are two major projects that extends its functionality.
Usermin: This module is used to extend the user level functions such as webmail, password changing, mail filters and much more.
Virtualmin: It is a web hosting control panel which provides simple and elegant interface for users to manage and host their websites and to manage multiple virtual hosts.