The following modules can help improve the accessibility of your site.
The Accessibility (a11y) Checklist module is designed to help web developers step through some basic accessibility tests for reviewing their website. Like the other checklists, it's an important way to keep track of things to review.
The Accessible module is designed to help overcome deficits in Drupal 6 core and contributed modules without theming and coding. It works through form hooks, CSS additions, and theming.
- Adds ability for block authors to class individual block titles as off-screen.
- Fixes Google CSE search form label and heading accessibility issues through hook form alter.
Accessible Content (D6)
The Accessible Content module helps create content that meets accessibility standards, and lets site administrators build and customize standards the site should adhere to. When the module is enabled, it creates two kinds of nodes, a collection of Accessibility Tests (you can view a list of all the available tests, and the reason why this is done), and a group of these tests called Accessibility Guidelines. Using the QUAIL project library this module leverages the Open Accessibility Checks which can help run automated tests for WCAG 1.0, WCAG 2.0, and Section 508 guidelines.
Quail API (D7)
Provides an API for the 3rd-party Quail Library to drupal modules. Quail API is a complete rewrite of parts of the Drupal 6 project called "Accessible Content".
The Quail Library is a 3rd-party PHP project located at: quail-lib.org and code.google.com/p/quail-lib/. This 3rd-party libary provides accessiblity validation for common web-accessiblity standards, such as: Section 508 and WCAG 2. Unlike other web accessiblity scanners, such as WAVE (wave.webaim.org), the Quail Library includes context-specific validation. This validation is a double-edged sword in that it helps catch and identify far more violations to a given standard but at the cost of producing more false positives.
This module is designed to help copywriters and editors develop more consistently readable content across a Drupal site. It performs five popular automated readability tests that provide a grade level equivalency of the difficulty of a page's readability.
Better Select (D6)
Multi-select HTML select elements are hard for users. Selecting more than one requires Ctrl+clicking (or Cmd+clicking on Mac), and explaining this to users who sometimes have trouble even clicking the mouse at all is no one's idea of fun.
Better Select module overrides all multi-select HTML elements in Drupal and replaces them with checkboxes, in an auto-scrolling div so they don't take up much room on the page.
Inspired by Block Class, this module adds additional elements to the block configuration forms that allow users to assign a ARIA landmark role to a block.
The Text Resize module provides your end-users with a block that can be used to quickly change the font size of text on your Drupal site. The block includes two buttons that can increase and decrease the printed text on the page. This module is primarily focused on increasing the accessibility of your pages, by helping visually-impaired users to adjust the text size so that it is most comfortable for their eyesight.
The Switchtheme module adds a block to allow users to switch between enabled themes. Themes can be given 'user friendly' names and access can be controlled by user role.
The htmLawed module enables the use of the htmLawed (X)HTML filter/purifier PHP script as an input filter with input format-, content (node) type- and body/comment/teaser-specific configurations.
HTML Purifier is a standards-compliant HTML filter library. HTML Purifier will not only remove all malicious code (better known as XSS) with a thoroughly audited, secure, yet permissive whitelist, it will also make sure your documents are standards compliant, something only achievable with a comprehensive knowledge of W3C's specifications.
This module tidies Drupal's HTML output with HTML Tidy by optionally sanitizing it when it is saved or when it is displayed, like a traditional input formatter. Missing and mis-ordered tag components are replaced and reordered automatically so that user input doesn't break site structure with open tags and the like.
* There is some debate as to whether text resize icons are more than a crutch for users. Considering most browsers do a better job of resizing the text than any web page will, some of us advocate for teaching users how to use their browser properly.
For more information about these modules see the accessibility group wiki page.