LinkChecker - LinkChecker is a free, GPL licensed website validator.
Check a Site - Scan websites for over 700 quality problems
DRKSpiderJava - DRKSpider is an open source website crawler (sitemap generator) and link checker. Features:
Beta Family - 50,000 testers to test your app
Dead Link Checker - Check for broken links on any website
Sqreen - Sqreen is a web application security monitoring and protection solution helping companies protect their apps and users from attacks. Get started in minutes.