tota11y - An accessibility visualization toolkit from Khan Academy
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.
Colorific - Colorific Hair Color Salons give you amazing color at an affordable price.
Page Speaker - Modern web accessibility tools for agencies & webmasters
HTML Validator - HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla.
accessiBe - Making websites accessible to people with disabilities