Proxy software

AlchemyPoint is a user-programmable mashup proxy server that can be used to re-write web pages, emails, instant messenger messages, and other network transmissions on the fly.
The Apache HTTP Server can be configured to act as a proxy server.
Blue Coat's (formerly Cacheflow's) purpose-built SGOS proxies 15 protocols including HTTPS/SSL, has an extensive policy engine and runs on a range of appliances from branch-office to enterprise.
EZproxy is a URL-rewriting web proxy designed primarily for providing remote access to sites that authenticate users by IP address.
JAP - A local proxy, web anonymizer software connecting to proxy server chains of different organisations
Microsoft Internet Security and Acceleration Server is a product that runs on Windows 2000/2003 servers and combines the functions of both a proxy server and a firewall.
Nginx Web and Reverse proxy server, that can act as POP3 proxy server.
Polipo is a small, fast, open source caching web proxy with some unique features.
Privoxy is a free, open source web proxy with privacy and ad-blocking features.
Proxomitron - User-configurable web proxy used to re-write web pages on the fly. Most noted for blocking ads, but has many other useful features.
SafeSquid Linux based, complete content filtering HTTP1.1 proxy, allows distribution of 'profiled' internet access.
SSH Secure Shell can be configured to proxify a connection, by setting up a SOCKS proxy on the client, and tunneling the traffic through the SSH connection.
Sun Java System Web Proxy Server is a caching proxy server running on Solaris, Linux and Windows servers that supports HTTP/S, NSAPI I/O filters, dynamic reconfiguration, SOCKSv5 and reverse proxy.
Squid cache is a popular HTTP proxy server in the UNIX/Linux world.
Tor - A proxy-based anonymizing Internet communication system.
Varnish is designed to be a high-performance caching reverse proxy.
WinGate is a multi-protocol proxy server and NAT solution that can be used to redirect any kind of traffic on a Microsoft Windows host. It also provides firewall, VPN and mail server functionality. Its WWW proxy supports integrated windows authentication, intercepting proxy, and multi-host reverse-proxying.
WWWOFFLE has been around since the mid-1990s, and was developed for storing online data for offline use.
yProxy is an NNTP proxy server that converts yEnc encoded message attachments to UUEncoding, complete with SSL client support.
Ziproxy is a non-caching proxy for acceleration purposes. It recompresses pictures and optimizes HTML code, among other features.