Polipo!

Privoxy is a non-caching web proxy with advanced filtering capabilities for enhancing privacy, modifying web page data and HTTP headers, controlling access, and removing ads and other obnoxious Internet junk. Privoxy has a flexible configuration and can be customized to suit individual needs and tastes. It has application for both stand-alone systems and multi-user networks.

For those who have not yet been introduced, meet the Proxomitron: a free, highly flexible, user-configurable, small but very powerful, local HTTP web-filtering proxy. To become better acquainted, please see our online version of the Proxomitron Help files for a more comprehensive overview.

Karma Blocker is a lightweight ad blocker which is directed towards the more technically advanced users and gives great flexibility to block elements with its custom rules. It uses a Karma (or score) based weighting of objects, similar to popular spam filtering solutions like SpamAssasin.

The problem with other ad-blockers for Safari is that they are implemented as awful hacks: as an InputManager and/or ApplicationEnhancer. This compromises the stability of Safari and very often create problems when Apple releases a new version of Safari. Snow Leopard doesnt support the InputManager-based blockers when Safari runs in 64-bit mode.

Better Pop Up Blocker improves the default pop up blockers for Google Chrome and Apple Safari by blocking pop up windows opened by javascript, & other annoyances like alert, prompt, and confirm boxes. These popups often occur when you simply click on what looks like blank space or text that shouldn't do anything, let alone annoy you with a pop up window.

Tinyproxy is a light-weight HTTP/HTTPS proxy daemon for POSIX operating systems. It is free software, and supports transparent and reverse proxying.

Quero AdBlock IE XML is an InPrivate Filtering XML-based Ad Blocker for Internet Explorer 8 and Quero AdBlock IE TPL is an ad blocking Tracking Protection List (TPL) for Internet Explorer 9.Both are based on the Adblock Plus EasyList.

NoAds is an adblocking extension for the Opera web browser.

Lusca is a fork of the Squid -2 development tree. The Lusca project aims to fix the shortcomings in the Squid-2 codebase whilst maintaining the the Squid-2 functionality and stability.

Formerly a commercial product, Yahoo! donated it to the Apache Foundation, and it is now an Apache TLP.

WinGate Proxy Server is a highly capable integrated Proxy server, firewall and email server designed for access control, security and communications needs. What you do get is all the features of Standard license for 3 concurrent users.

SquidMan is a MacOS X graphical installer and manager for the Squid proxy cache. It is designed to operate as a "personal" proxy server.

ExaProxy is a a high-performance non-caching proxy. It is able to filter HTTP traffic using third party scripts in your favorite programming language.

gate - Performance & scalable I/O forward & reverse HTTP proxy based on node.js + V8 a real alternative to Squid & NGINX