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.
Epilepsy Blocker - Block flashing GIFs that may cause an epileptic seizure
Accessible Brand Colors - A tool to make sure your brand colors are ADA compliant.
Colorbox.io - Create accessible color systems 🎨
Page Speaker - Modern web accessibility tools for agencies & webmasters
Coblis - If you are not suffering from a color vision deficiency it is very hard to imagine how it looks...