The following modules can help improve the accessibility of your Drupal 8 site.
This list is based off the Drupal 8 documentation page Contributed Modules for Extending Accessibility in Drupal 8.
Add to Any
8.x-1.8
The Add to Any module allows users to share buttons for Drupal including the AddToAny universal share button, Facebook, Twitter, Google+, Pinterest, WhatsApp and many more.
Automatic Alternative Text
8.x-1.0-alpha2
The module uses the Microsoft Azure Cognitive Services API to generate an Alternative Text for images when no Alternative Text has been provided by user.
Block ARIA Landmark Roles
8.x-1.1
Inspired by Block Class, the Block ARIA Landmark Roles module adds additional elements to the block configuration forms that allow users to assign a ARIA landmark role to a block.
CKEditor Abbreviation
8.x-1.1
Adds a button to CKEditor for inserting and editing abbreviations. If an existing abbr tag is selected, the context menu also contains a link to edit the abbreviation.
CKEditor Accessibility Checker*
8.x-1.0
The CKEditor Accessibility Checker module enables the Accessibility Checker plugin from CKEditor.com in your WYSIWYG. This plugin is an innovative solution that lets you inspect the accessibility level of content created in CKEditor and immediately solve any accessibility issues that are found.
*Note: this module is now outside the Drupal security best practices, since it uses QuailJS which isn’t supported any more.
Fluidproject UI Options
8.x-1.2
Fluidproject's UI Options provides accessibility options for users to modify a page's font size, line height, font style, contrast, and link style. The changes are retained using cookies.
High Contrast (beta)
8.x-1.0-beta1
The High Contrast module provides a quick solution to allow the user to switch between the active theme and a high contrast version of it.
htmLawed
8.x-3.2
The htmLawed module uses the htmLawed PHP library to restrict and purify HTML for compliance with site administrator policy and standards and for security. Use of the htmLawed library allows for highly customizable control of HTML markup.
Siteimprove
8.x-1.0, 8.x-1.x-dev
The Siteimprove plugin bridges the gap between Drupal and the Siteimprove Intelligence Platform.
Thanks to the seamless integration, you are now able to put your Siteimprove results to use where they are most valuable – during your content creation and editing process.
Style Switcher
8.x-2.0-alpha1, 8.x-2.x-dev
The module takes the fuss out of creating themes or building sites with alternate stylesheets. Themer can provide a theme with alternate stylesheets. Site builder can add other alternate stylesheets right in the admin section. And this module presents all those styles as a block with links. So any site user is able to choose the style of the site he/she prefers.
Text Resize
8.x-1.1
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.