Virusdie - All-in-One cloud-based, simple, powerful and gorgeous website security tools built for everyone.
Dr. Link Check - Broken link checker with malware and parked domain detection
Checkbot - Checkbot will boost the SEO, speed and security of your site by checking you're following 50+ web best practices. Browser extension with free and paid plans.
BrokenLinkCheck - Free Broken Link Checker / Online Dead Link Checking Tool - find bad hyperlinks
Chaos Toolkit - A chaos engineering toolkit to help you build confidence in your software system
LinkChecker - LinkChecker is a free, GPL licensed website validator.