The A11Y Project is an irreplaceable website whose goal is to make websites (and other digital resources) accessible.
The website provides comprehensive checklists created using Web Content Accessibility Guidelines (WCAG). It also has a list of resources that includes software, books, blogs, and online tools developers can use to improve their websites’ accessibility. Finally, the A11Y Project maintains a blog that features posts about assistive technology, misconceptions about accessibility, quick tips for creating accessible content, posts written by people with disabilities, and more.