Dr. Link Check - Broken link checker with malware and parked domain detection
Ahrefs Backlink Checker - With the world's biggest index of live backlinks (over 15 trillion), Ahrefs Backlink Checker will show you the most complete backlink profile for any website.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Backlinks by Neil Patel - A backlinks research tool for competitive intelligence
SiteInspector - Catch spelling/grammar errors and broken links on websites.
Toxic Backlink Checker - Find out what's lurking in your backlink profile.