What is Webmin?
Webmin is a GUI based server administration tool for Linux/Unix systems.
Webmin is now under a BSD-like license, meaning that it may be freely distributed and modified for commercial and non-commercial use. It runs from a Perl based web server running on port 10000. It's also module based system so due to it's license structure anybody can create and distribute their own modules for Webmin. The lead developer is Jamie Cameron and updates for security and added features/functionality are frequent and well maintained.
It's designed to edit system files directly through the GUI using the built in web server and a number of CGI programs. It is good fit for existing infrastructure as it does not take over control of the system as do some other server admin tools so editing a config file through Webmin is no different that editing and saving that file though the CLI. This makes it an excellent learning tool for new system administrators as it lets them learn the entire system in a graphical format allowing them an easier transition to complete CLI administration. It also makes it easy for seasoned system administrators to do some time consuming tasks more quickly.
Webmin is often installed in combination with Virtualmin creating a complete seamless interface to manage the server and create and manage domains.
Communication with the developers and other users can be done through their forums