Site Rank Data - View historical rank information of websites via time series charts.
Xenu's Link Sleuth - Xenus Link Sleuth checks Web sites for broken links.
HypeStat - HypeStat is free statistics and analytics service, where you can find information about every website.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Q-Stats - Get free marketing insights for every question on Quora.
Integrity - Feature comparison of link checkers for Mac: Integrity, Integrity Plus and Scrutiny