Squid
Squid is a high-performance proxy caching server for web clients, supporting FTP, gopher, and HTTP data objects. Unlike traditional caching software, Squid handles all requests in a single, non-blocking, I/O-driven process.

http://www.squid-cache.org

Dans Guardian
Dan's Guardian is a content filtering mechanism that controls access to the web. The content phrase filtering will check for pages that contain profanities and phrases often associated with pornography and other undesirable content.

http://dansguardian.org/