SafeSquid: Content Filtering Internet Proxy, has released a full-
featured FREE edition with no time limit that can comfortably be used
in a 20 user network for 'Total Access Control' and 'Total Content
Control' (may not be bundled within any S/W H/W appliances, without
prior consent from OEIPL)

SafeSquid is an anti virus and content filtering proxy server. It has
many advanced features such as URL blacklists, bandwidth management,
regular expression substitution on Website content and requested URLs,
ICP and CARP support for inter operating with other proxy servers,
configuration synchronization to ease management in a cluster, ICAP
support for using third-party content adaptation software, image and
link pre-fetching, HTTP and FTP content caching, PAM authentication,
filters like Cookie Filter, MiMe filter, Header Filter and an
intuitive Web interface for configuration.

To download the free version, register on the SafeSquid Forum at
http://www.safesquid.com/forum/ and use your forum ID to download
http://downloads.safesquid.net/free/safesquid-4.1.1-com20-free.tar.gz

Feel free to use the forum for any technical assistance.