Dr. Link Check - Broken link checker with malware and parked domain detection
tota11y - An accessibility visualization toolkit from Khan Academy
BrokenLinkCheck - Free Broken Link Checker / Online Dead Link Checking Tool - find bad hyperlinks
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.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Page Speaker - Modern web accessibility tools for agencies & webmasters