Brokenlinks is a tool to help you find and track Broken links on your website, namely URLs that no longer point to anything useful. It is a back end to the Xenu Link Sleuth broken link detector that compensates for Xenu's weakness of overwhelming you with reports of links that are not really broken.
Brokenlinks retests ostensibly broken links and maintains a database of link integrity History. It partly compensates for various bugs and deficiencies in Xenu.