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:
Backlink Tool - A backlink tool to index your links quickly and freely.
Dead Link Checker - Check for broken links on any website
SEMScoop - Find and analyze easy to rank long-tail keywords with free SEMScoop Keyword Difficulty Tool, Start using them for SEO, PPC, content creation and all your marketing activities