Frox is a transparent FTP proxy that runs under Linux and *BSD. It should also work on other UNIX OSes that use ipfilter. It supports caching of FTP downloads, either by redirecting through a Squid proxy, or through its own local cache. Downloads may also be transparently scanned for viruses (through an external scanner). Additionally there is an interface for writing scripts to add features or modify frox's behavior, and examples are included to limit download file size and to transparently direct connections to specific hosts to mirror servers. The proxy is written with security in mind, and in the default setup runs as a non-root user in a chroot jail.
jftpgw is a proxy server for the FTP protocol. It is highly configurable, allowing you to use an XML-like configuration file to define almost any combination of the client's IP, the server's IP, the user name, the destination port, and so on. jftpgw supports inetd/daemon mode, transparent proxying, forwards, caching, logging, data IP and port specification (port ranges), limiting of the number of simultaeous sessions, and several proxy login styles for clients that support FTP proxies.
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 WWWOFFLE programs simplify World Wide Web browsing from computers that use intermittent (dialup) connections to the Internet. It is a simple proxy server with special features for use with dial-up Internet links. It makes it possible to browse Web pages and read them without having to remain connected. There are too many features to mention, but they include privacy control, cookie/advert blocking, efficient bandwidth usage by specifying intervals between refreshes, options to monitor pages regularly, recursive fetching, HTML cleaning, highlighting of cached links, indexes of cached pages, searching of cached pages, and many more.