skipfish
A fully automated, active web application security reconnaissance tool. Key features:
High speed: pure C code, highly optimized HTTP handling, minimal CPU footprint - easily achieving 2000 requests per second with responsive targets.
Ease of use: heuristics to support a variety of quirky web frameworks and mixed-technology sites, with automatic learning capabilities, on-the-fly wordlist creation, and form autocompletion.
Cutting-edge security logic: high quality, low false positive, differential security checks, capable of spotting a range of subtle flaws, including blind injection vectors.
The post announing the tool:
https://googleonlinesecurity.blogspot.com/2010/03/meet-skipfish-our-automated-web.html
The project page at google code:
https://code.google.com/p/skipfish/
Skipfish documentation:
https://code.google.com/p/skipfish/wiki/SkipfishDoc
The tool is written by lcamtuf, who joined google a few years ago. :)