DeleGate is a multi-purpose application level gateway or proxy server that mediates communication of various protocols, applying cache and conversion for mediated data, controlling access from clients, and routing toward servers. It translates protocols between clients and servers, converting between IPv4 and IPv6, applying SSL (TLS) to arbitrary protocols, merging several servers into a single server view with aliasing and filtering. It can be used as a simple origin server for some protocols (HTTP, FTP, and NNTP).
The stunnel program is designed to work as an SSL encryption wrapper between remote client and local (inetd-startable) or remote server. It can be used to add SSL functionality to commonly used inetd daemons like POP2, POP3, and IMAP servers without any changes in the programs' code. It will negotiate an SSL connection using the OpenSSL or SSLeay libraries. It calls the underlying crypto libraries, so stunnel supports whatever cryptographic algorithms you compiled into your crypto package.
FreeRADIUS is a high-performance, highly configurable, and feature-rich RADIUS server. Supported features include EAP (wireless authentication, PEAP, TTLS), MySQL, PostgreSQL, Oracle, LDAP, X9.9 token cards, VMPS, and many more. It comes with more than 50 vendor dictionaries, and interoperates with many others. It is the only open source RADIUS server that has implemented EAP, and it is currently deployed in multiple million-user systems.
Proxytunnel is a program that connects stdin and stdout to a server somewhere in the Internet through an industry standard HTTPS proxy. It's mostly used as a backend for OpenSSH's ProxyCommand, and as a proxy backend for Putty. It can also be used for other proxy-traversing purposes.
Privoxy is a Web proxy based on Internet Junkbuster with advanced filtering capabilities for protecting privacy, filtering Web page content, managing cookies, controlling access, and removing ads, banners, pop-ups, and other obnoxious Internet junk. Privoxy has a very flexible configuration and can be customized to suit individual needs and tastes. Privoxy is useful for both stand-alone systems and multi-user networks.
Tor is a network of virtual tunnels that allows people and groups to improve their privacy and security on the Internet. It also enables software developers to create new communication tools with built-in privacy features. It provides the foundation for a range of applications that allow organizations and individuals to share information over public networks without compromising their privacy. Individuals can use it to keep remote Websites from tracking them and their family members. They can also use it to connect to resources such as news sites or instant messaging services that are blocked by their local Internet service providers (ISPs).
Stone is an application layer TCP/IP packet repeater. It repeats TCP and UDP packets from the inside of a firewall to the outside or vice versa. It is simple, supports OpenSSL for encrypting and decrypting packets, performing client and server verifications, and sending a substring of the subject of the certificate to the destination, can operate as an HTTP proxy, and performs POP to APOP conversion. It also supports IPv6 and can convert between IPv4 and IPv6 each other.
Cyan Secure Web Proxy Server is a carrier grade, high performance Internet filtering proxy server for Linux. It includes scalable (user/group/host) Web filter and virus scan utilities for blocking malicious applications at the gateway. It has an advanced URL database, authentication support (Active Directory, LDAP, NTLM), SSL Interception, easy deployment, and remote administration.