FilterProxy is a Perl script that acts as a generic Web proxy. It is unique in that it allows you to install modules that can perform arbitrary transformations on HTML (or any other MIME-type) and HTTP headers. It filters ads by stripping HTML from the page, anonymizes requests by removing Referer and User-Agent headers, compresses HTML content, and de-animates animated gifs. Configuration is done via Web-based forms or editing a Perl data structure.
SmoothWall Express is a network firewall, designed with home and small business users in mind. It is based upon a security-hardened subset of the GNU/Linux operating system and is completely free to use, download, and distribute. SmoothWall Express offers facilities and features normally only seen in expensive commercial offerings.
squid_redirect uses a list of patterns to zap annoying ad banners from Web pages, inserting a placeholder image. It lives in a Web proxy and so requires no special browser facilities. It's readily customizable, small, fast, and easy to install. (In Debian/Ubuntu, this program is named "adzapper".)
Anti-censorship tools (proxyTools) consists of a huge Perl application (localProxy) and a set of tools to analyze the user's network (proxies, firewall rules, name servers, etc.). LocalProxy abstracts external services in an uncensored, reliable, fast manner to the localhost, where they may be used by standard clients (Web browsers, Usenet news clients, SOCKS-capable clients, etc.). Various combinations of strategies are tried to ensure the non-censored nature of the information, and multiple, parallel services (e.g. HTTP proxies) are used to ensure reliability and speed. The tools are capable of automating collection of the data required for localProxy. LocalProxy builds a configuration for the user and dynamically adjusts to using the fastest strategies and proxies available to it. The tools are useful for network analysis (firewall rules, proxy capabilities, etc.) independently of localProxy.
The DansGuardian Anti-Virus Scanner gives you the ability to virus-scan all content that passes through DansGuardian. It uses the scanning code from the MailScanner project to do the actual virus scanning, so it supports all the virus engines that the MailScanner project supports. The scanning is done as the file is being downloaded, so your current network apps don't have to be modified, etc. They just have to support using a proxy.
fk_html is a standard filter for incoming mail. It runs on your local machine as a fake POP3 server that redirects your mail client connections to your real POP3 server. Doing that it can scan, filter, and convert your incoming emails and is totally independent from your mail client type or version It provides multiple account settings, conversion from HTML mail to plaintext mail, removal of scripts from HTML mail and attachments, address filtering based on blocklist and allowlist, the ability to apply different policies to different accounts, and SSL support (also for non-secure clients, in which case only the loopback connection is not encrypted).