Administrative tools in Debian range from small tools that administrate small portions of the system(like fdisk) to complete system administrative tools such as linuxconf and Webmin.

Some Handy Small Tools

rcconf -- Allows one to easly configure which daemons are to be started at boot time. For example if you don't want to be presented with a graphical login after booting you can uncheck xdm, gdm, and/or kdm.

modconf -- Modconf provides a GUI for installing and configuring device driver modules

["cfengine"] -- Provides a "rule engine" where you describe how your system(s) are to be configured/managed, and it goes off and applies these rules, doing incremental updates to system configuration.