Backframe is a full-featured attack console for exploiting WEB browsers, WEB users and WEB applications. Backframe was started as a pet projected of mine called Backweb. Because Backweb is a registered trademark of Backweb Technologies, the application name has changed since then to what it is today.
Backframe is very extensible attack console, resembling all features from a class of tools known as XSS proxies. The actual framework contains a lot of more features. Developers can extend virtually every aspect of the Backframe environment. You can write inline scripts/profiles which are loaded when the application starts and as such guarantee maximum extensibility.
UPDATE 09/05/2011: We've stopped supporting the online version. However, you can still download the sources from the public SVN repository over here.