LinkChecker - LinkChecker is a free, GPL licensed website validator.
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.
DRKSpiderJava - DRKSpider is an open source website crawler (sitemap generator) and link checker. Features:
Whatsmyserp - Powerful Rank & Serp Tracking. Completely Free.
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
Backlink Tool - A backlink tool to index your links quickly and freely.