WebScarab is a framework for analysing applications that communicate
using the HTTP and HTTPS protocols. In its most common usage,
WebScarab operates as an intercepting proxy, allowing the user to
review and modify requests created by the browser before they are
sent to the server, and to review and modify responses returned
from the server before they are received by the browser.

WWW: http://www.owasp.org/index.php/Category:OWASP_WebScarab_Project