Web accessibility refers to the ease with which people can access all of the content on your website. Accessibility is often thought of in relation to disabilities such as blindness, deafness, ADD and ADHD, color blindness, etc. However accessibility is important to all users of your site, if you would like to engage them, inform them, encourage them to purchase products, etc.
Until recently there were guidelines for accessibility such as Section 508 Information Technology Accessibility Standards and W3C Web Content Accessibility Guidelines but no testing sites, which makes it hard for web designers to easily improve their sites, based on the feedback provided by testing sites.
The University of Illinois has just launched the Illinois Functional Web Accessibility Evaluator 1.0 (FAE), a testing site that addresses this need. Web designers and developers can register for free accounts which allows us to test whole sites, not just single pages. Highly recommended!