In computer networks, a ‘proxy server’ is a server that acts as a go-between for requests from clients (Web browsers on a PC) seeking resources from other servers.

It may serve the request without contacting the specified server. In this case, it 'caches' responses from the remote server, and returns subsequent requests for the same content directly.

The purpose of using a proxy is to speed up access to a resource (via caching). It is commonly used to cache Web pages from a Web server. A proxy server can be placed in the user's local computer or at various points between the user and the destination servers or the Internet.

Caching proxies keep local copies of frequently requested resources, allowing large organizations to significantly reduce their upstream bandwidth usage and cost, while significantly increasing performance.

Below are some of the more commonly used Proxy software packages and links to them. You can read their manuals to help you to setup a proxy at your location.

Free and Open Source Software

• The Apache HTTP Server can be configured to act as a proxy server.
• Delegate (networking) is a multi-purpose application level gateway, or a proxy server which runs on multiple platforms.
• I2P (multiple licenses) - A proxy-like decentralized network for anonymizing Internet data transfers.
• Nginx Web and Reverse proxy server, that can act as POP3 proxy server.
• PHProxy is one of the oldest and most customized proxy scripts in use on the Internet. Many of the newer proxy scripts were inspired by PHProxy.
• Pound (networking) is a reverse proxy, load balancer and HTTPS front-end for Web server(s).
• Privoxy is a free, open source Web proxy with privacy and ad-blocking features.
• Squid is a popular HTTP proxy server in the UNIX/Linux world.
• Tinyproxy is a light-weight HTTP proxy daemon ideal for embedded use on POSIX operating systems.
• Tor - A proxy-based anonymizing Internet communication system.
• Varnish is designed to be a high-performance caching reverse proxy.
• WWWOFFLE has been around since the mid-1990s, and was developed for storing online data for offline use.
• Ziproxy is a non-caching proxy for acceleration purposes. It recompresses pictures and optimizes HTML code.

Proprietary Software

• 3proxy is a freeware proxy server, previously known as 3APA3A, and works on Windows and Linux/Unix.
• AlchemyPoint is a user-programmable mashup proxy server that can be used to re-write Web pages, e-mails, instant messenger messages, and other network transmissions on the fly.
• 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.
• Charles is a Java-based user-configurable HTTP proxy/HTTP monitor/Reverse Proxy that can be used with Flash Remoting (AMF0 and AMF3).
• CACHEbox is a high performance HTTP/HTTPS/FTP caching proxy appliance supporting forward and reverse deployment modes.
• CGIProxy, Web-based proxy script written in Perl. Free for non-commercial use.
• EZproxy is a URL-rewriting Web proxy designed primarily for providing remote access to sites that authenticate users by IP address.
• HTTP-Tunnel is a freeware proxy client, to proxy any site, p2p, IM and game. Allows you to be monitor free. SOCK and HTTP protocols.
• Ideco Gateway - Linux based multi-protocol proxy server with GUI configuration tool and NAT/VPN support.
• JAP - A local proxy, Web anonymizer software connecting to proxy server chains of different organizations
• Microsoft ISA server is described by Microsoft as an "integrated edge security gateway"; it includes caching Web proxy, caching reverse proxy, Firewall, VPN, NAT, content filter, SSL encryption, and other components.
• Novell BorderManager Web proxy server, reverse proxy, Firewall and VPN end point.
• 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 HTTP 1.1 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://https, NSAPI I/O filters, dynamic reconfiguration, SOCKSv5 and reverse proxy.
• TcpCatcher is a free TCP and HTTP(S) proxy server for educational purposes. It allows you to modify packets on the fly.
• 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.
• yProxy is an NNTP proxy server that converts yEnc encoded message attachments to UUEncoding, complete with SSL client support.
• Zeus functions as both a forward and reverse proxy server. It operates on Solaris, FreeBSD and Linux.