content scanning web filter
E2Guardian is a web proxy that filters the actual content of pages based on various methods including phrase matching, PICS filtering and URL filtering. E2Guardian is designed to be completely flexible and allows you to tailor the filtering to your exact needs. It can be as draconian or as unobstructive as you want. The default settings are geared towards what a primary school might want but E2Guardian puts you in control of what you want to block.
Homepage: http://www.e2guardian.org/