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. 

WWW: http://code.google.com/p/skipfish