Ebox is a free (open source) web based Linux server management tool.
From the project home page:
Ebox management tool will effectively and easily help you managing the advanced services for your corporate network. Designed with extensibility in mind it offers, among others, these modules:
=> Transparent proxy
=> Content filter
=> NTP Server
=> Users and groups administration
=>Mail server etc
On a related note there is nice article written using ebox at howtoforge:
"This article shows how to run a file-, print-, HTTP proxy- DHCP-, and time server for small and medium enterprises (SME) on one single Debian Sarge system.
eBox was developed to administrate advanced services for corporate networks, and it was created for Debian Sarge."