Ever find yourself looking for that showstopper exploit in a Web-app, and forgetting to check out all the low-hanging fruit? That's intitially why we created Watcher. For one thing, we don't want to manually inspect a Web-app for many of these issues (cookie settings, SSL configuration, information leaks, etc), but we still want to find and fix them. Watcher provides this level of security analysis, plus provides hot-spot detection to help pen-testers focus in on the spots that will lead to that showstopper exploit.
Watcher is a Fiddler addon which aims to assist penetration testers in passively finding Web-application vulnerabilities. The security field today has several good choices for HTTP proxies which assist auditors and pen-testers.
We chose to implement this as a plugin for Fiddler which already provides the proxy framework for HTTP debugging.