WAI-ARIA, the Accessible Rich Internet Applications Suite, defines a way to make Web content and Web applications more accessible to people with disabilities. It especially helps with dynamic content and advanced user interface controls developed with Aja
W3C link checking service. Feed it your URL and some options. The output format is not exactly "user-friendly", but it is clever enough to obey robots.txt when checking links.
The WCAG Samurai was a group of developers, led by Joe Clark, that publishes corrections for, and extensions to, the Web Content Accessibility Guidelines 1.0.