accessiBe - Making websites accessible to people with disabilities
Nibbler - Free tool for testing how good your website is, and what you can do to improve it. Check accessibility, SEO, social media, compliance and more.
tota11y - An accessibility visualization toolkit from Khan Academy
Contraste - Check the accessibility of text against the WCAG.
Page Speaker - Modern web accessibility tools for agencies & webmasters
RoRvsWild theme - Colors for developers with sensitive eyes