Dante is a free implementation of the proxy protocols SOCKS version 4 and SOCKS version 5 (RFC 1928). It can be used as a firewall between networks, controlling outgoing traffic. The package consists of two parts: a socks server and a proxy client that supports socks, HTTP proxies, and UPnP. RFC 1961 (GSSAPI) is supported in both the client and the server. Commercial support is available.
PHP-Proxy is a PHP script for taking Web pages from one server, so that your main server is protected if the Web server is overloaded from things like DOS attacks. It is also very useful if you have a machine behind a firewall that you want to be your server for Web pages, provided that the machine running the proxy has port 80 open. Finally, there is encryption to defeat filters on specific words if need be.
Charles is a Web debugging tool, HTTP monitor, and reverse HTTP proxy for Web developers that includes plain text debugging of HTTPS/SSL. It is built in Java Swing, and runs on all Java platforms. It is an HTTP proxy server that displays requests and responses, complete with HTTP headers. This enables the developer to examine the exact content of HTTP exchanges, including cookies, caching, and redirects. It can also throttle your connection in order to simulate modem conditions. It is a valuable tool for all Web developers and is especially useful for debugging XML RCP, SOAP, Web services, AJAX/XMLHTTP, and Macromedia Flash client-server traffic including AMF, AMF 3, LoadVars, and XML Sockets.
Burp proxy is an interactive HTTP/S proxy server for attacking Web-enabled applications. It operates as a man-in-the-middle between the end browser and the target Web server, and allows the attacker to intercept, inspect, and modify the raw traffic passing in both directions. Text and hex editing may be performed on intercepted traffic. Downstream proxies are supported. Authentication may be done to downstream proxy and Web servers, using basic, NTLM, or digest authentication types.
EXProxy is a simple HTTP/HTTPS proxy server packaged as a Java library and designed to listen to HTTP requests and responses going through it. It has also the ability to modify requests and responses on the fly. For HTTP over SSL, it uses the "man in the middle" principle, and so will generate warnings about certificates in your Web browser.