In 1995, CAST launched Bobby as a free public service to make the burgeoning World Wide Web more accessible to individuals with disabilities. Over the next decade, Bobby helped novice and professional Web designers analyze and make improvements to millions of Web pages. This work won CAST numerous awards and international recognition.
CAST no longer supports the Bobby accessiblity testing software. Bobby was sold to Watchfire in 2004 which, in turn, was acquired by IBM in 2007.
Although Bobby is no longer available as a free service or standalone product, it is one of the tests included within the IBM Rational Policy Tester Accessibility Edition software, the comprehensive enterprise application for testing websites.
References:
http://www-306.ibm.com/software/rational/welcome/watchfire/press.html
http://www.watchfire.com/products/webxm/bobby.aspx
http://www-306.ibm.com/software/awdtools/tester/policy/accessibility/
Other options are listed on the W3C Website at:
http://www.w3.org/WAI/eval/Overview.html