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.
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).
Jonama is a piece of software acting as a relay between a client over the Net and your internal systems. It was developed which security in mind, ie. it makes use of the SSL protocol to identify remotes and crypt channels and uses Unix mechanisms like chroot and setuid to minimize rights and actions.
PET is a proxy server that works for HTTP (with caching), SSL, and FTP. PET supports extended ICP services (enhanced algorithms) and Cache Digests, both of which are compatible with Squid. It also includes an easy-to-use Web-based configuration interface for nearly all configuration parameters and statistics.
RabbIt is a mutating, caching Web proxy used to speed up surfing over slow links like modems. It does this by removing advertising and background images and scaling down images to low quality JPEGs. RabbIT is written in Java and should be able to run on any platform. It does depend upon an image converter if image scaling is on. The recommended image converter is "convert" from the ImageMagick package.
squid_redirect uses a list of patterns to zap annoying ad banners from Web pages, inserting a placeholder image. It lives in a Web proxy and so requires no special browser facilities. It's readily customizable, small, fast, and easy to install. (In Debian/Ubuntu, this program is named "adzapper".)
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.