"A new update to the Watcher passive vulnerability detection and security testing tool has been released. Watcher is an open source addon to the Fiddler Web proxy that aids developers, auditors, and penetration testers in finding Web-application security issues as well as hot-spots for deeper review." - Casabasecurity

The full announcement can be found at http://www.casabasecurity.com/blog/.

Watcher Download: http://websecuritytool.codeplex.com/
Watcher FAQ: http://websecuritytool.codeplex.com/wikipage?title=FAQ&referringTitle=Home