Hostess is distributed in the Public Domain.
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Some of the best programs ever written were written out of need. I ran a computer lab at a community college for nearly a year. Getting tired of constantly kicking random students out of the computer lab for surfing pornographic websites (which was against school policy), I decided to take action and write a program that would assist in blocking said websites at a local machine level. As soon as it was implemented, the number of students getting kicked out of the computer lab went from five or more a week to zero for a good portion of a half year. I'm still in shock.
Takes a list of domain names from SquidGuard or compatible (and here's my favorite list) and outputs a hosts file suitable for blocking domains at the local machine level. Written in Java and requires a JRE. (From what I understand, it requires version 1.5, your mileage may vary.)
Note for those wishing to use the resultant host file on Windows, you may wish to do the following first, which appears to prevent a system stall once the host file is installed, in most situations.