Frox is a transparent FTP proxy that runs under Linux and *BSD. It should also work on other UNIX OSes that use ipfilter. It supports caching of FTP downloads, either by redirecting through a Squid proxy, or through its own local cache. Downloads may also be transparently scanned for viruses (through an external scanner). Additionally there is an interface for writing scripts to add features or modify frox's behavior, and examples are included to limit download file size and to transparently direct connections to specific hosts to mirror servers. The proxy is written with security in mind, and in the default setup runs as a non-root user in a chroot jail.
httpMonitor is a Python program which lets you monitor the HTTP traffic between a browser and a Web server. You configure your browser to use httpMonitor as its proxy to ensure that all HTTP traffic between browser and server goes via httpMonitor. In a XML-configuration file you can specify a Python-function as processor for the HTTP-messages you are interested in (requests or responses, which match certain criteria). You may have as many processors as you want, without modifying the actual program. The only thing you need to do is configure the httpMonitor and write your processors.
rproxy is an extension to HTTP which allows transferring of differences between a web server and client, using an algorithm similar to rsync's. This works particularly well for dynamically-generated sites, where the pages are often similar but not the same on each visit. Transferring just the difference reduces network traffic and therefore loading time.
Desproxy is tunneling proxy (using the CONNECT method, as used by HTTPS) with helper programs to use this proxy. These include a DNS server and a SOCKS4/SOCKS5 proxy, running with or without inetd for simple port forwarding with inetd. This allows you to use TCP applications (IRC, telnet, fetchmail, SSH, etc.) through your firewall proxy. Features include proxy authentification and multiplatform support.
Middleman is a robust proxy server with many features designed to remove unwanted content, increase privacy, and to simply make surfing the Web a more pleasant experience. Some of the highlights include banner and popup blocking, HTTP and FTP content caching, NTLM and Basic authentication when forwarding through another proxy server, regular expression substitution in downloaded files and HTTP headers, regular expression substitution on requested URLs, many URL commands to temporarily change the proxy settings or to view information about a requested file, complete support for HTTP/1.1 including persistent connections and gzip encoding, and an intutive Web interface for configuring the proxy.
Ziproxy is a high-performance forwarding (non-caching) HTTP proxy that gzips text and HTML files, and reduces the size of images by converting them to lower quality JPEGs or JPEG 2000. It is intended to increase the speed for low-speed Internet connections (mobile, dial-up, other). It's suitable for both home and professional usage. Ziproxy is fully configurable and also features transparent proxy mode, HTML/JS/CSS optimization, operation in daemon mode, a detailed access log with compression statistics, basic authentication, and more.
Libconnect is a simple library wrapper written in assembly language that intercepts the calls applications make to establish TCP connections and transparently proxies them as necessary. Existing applications can use this library without any recompilation or modification. If you provide multiple proxies they will be cycled connection after connection.