Skipfish - web application security scanner

Skipfish is an active web application security reconnaissance tool. It prepares an interactive sitemap for the targeted site by carrying out a recursive crawl and dictionary-based probes. The resulting map is then annotated with the output from a number of active (but hopefully non-disruptive) security checks. The final report generated by the tool is meant to serve as a foundation for professional web application security assessments.

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 tool is believed to support Linux, FreeBSD, MacOS X, and Windows (Cygwin) environments.