Polipo is a fast caching and small web proxy (a web cache, a proxy server, an HTTP proxy). While Polipo was designed to be used by one person or a small group of people, there is nothing that prevents it from being used by a larger group.
What Polipo is useful for
By virtue of being a (mostly) compliant HTTP/1.1 proxy, Polipo has all the uses of traditional web proxies. It is typically used as a web proxy for a single computer or a small network, although there's no fundamental reason why it shouldn't be used by a larger one.
Because Polipo is small and easy to install (just copy the polipo binary), it has applications beyond those of traditional web proxies. I usually copy Polipo to whatever machine I happen to be using and do all my browsing through it (with no on-disk cache). I've also occasionally used it to cross firewalls that were misconfigured or overly restrictive.
Because it has primitive filtering capabilities, Polipo can be used in place of ad-filtering, privacy-enhancing proxies such as Junkbuster, Privoxy or WWWOFFLE. As Polipo has much more refined HTTP support, it doesn't impose the speed tax usually associated with such proxies.
Since it can speak both IPv4 and IPv6, Polipo can be used as a bridge between the IPv4 and IPv6 Internets: to allow an IPv6-only host to access IPv4 servers or vice versa.
Since it can speak the SOCKS protocol, Polipo can be used together with the tor anonymising network.
Here are some key features of "Polipo":
· Polipo will use HTTP/1.1 pipelining if it believes that the remote server supports it, whether the incoming requests are pipelined or come in simultaneously on multiple connections (this is more than the simple usage of persistent connections, which is done by e.g. Squid);
· Polipo will cache the initial segment of an instance if the download has been interrupted, and, if necessary, complete it later using Range requests;
· Polipo will upgrade client requests to HTTP/1.1 even if they come in as HTTP/1.0, and up- or downgrade server replies to the client's capabilities (this may involve conversion to or from the HTTP/1.1 chunked encoding);
· Polipo has complete support for IPv6 (except for scoped (link-local) addresses).
· Polipo can optionally use a technique known as Poor Man's Multiplexing to reduce latency even further.