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.
It detects broken links and automatically corrects selected permanent or temporary redirects.
TidyURLs cleans up all the hrefs= and src= on your website. This help ReplaceURLs work properly.
ReplaceURLs patches URLs in your local website files to the new redirected values that BrokenLinks finds.
Read the brokenlinks manual on the mindprod site. It explains in more detail what it is for and how to use it.