This is the home of http_proxy. It's a very simple program to server as an http_proxy. The main usage that I have for it is that I fire it up when I have a problem with the interaction between the client (usually a web browser) and a web server. The proxy program spits out everything it gets from the client and everything it gets from the server so you can see exactly what's going back and forth, including all headers, posted data, etc.