Machilles is a freeware proxy server that allows the editing of outgoing HTTP requests. It is intended for use in testing Web applications, especially for security issues. It is similar to Achilles and PenProxy, the Windows applications. Currently, it allows user editing of HTTP header fields Cookie and User-Agent, as well as data sent in POST requests.
What's new in Machilles
Machilles now automatically sets up your OS to use its local proxy, so all you have to do is point and click (and possibly authenticate).
Now customize whether to intercept requests that have no refer field (default) or to intercept all requests.