This list contains a vast and available open source tools to find out broken links in your web site.

1. Alert LinkRunner
A Windows desktop link checker.
Big Brother
An open source link checker for Linux.
Broken Link Checker
Online service which checks a single page for broken links, missing images etc.
CSE HTML Validator
A Windows desktop application which validates (x)html / css etc. and can check links.
CyberSpyder Link Test
A Windows desktop utility.
Dead-Links.com
free online link checking service. Checks deeper into your site if a backlink is detected.
DeepTrawl
A Windows / Mac desktop application which checks for broken links and other types of errors.
Dreamweaver
Includes a link checking feature.
Free Link Checker
Free online service to check a single page for broken links.
Free Online Link Checker
Free online service which checks the links on a single page.
HTML Power Tools
A suite of Windows tools which includes a link validator.
InSite
A Windows desktop application which performs website spell checking and link validation.

2. Jenu
An open source Java copy of Xenu.
JSpider
An open source Java web spider which can search for broken links.
Link Alarm
A long established online link checking service.
Link Checker
A free online service from the W3C (the body responsible for web standards).
Link Checker
An open source link checker which includes command line, GUI and Web interfaces.
Link Checker Lite
The free version of "Web Link Validator".
Link Checker Pro
Windows desktop software which checks for broken links and creates visual site maps.
Link Lint
An open source Perl program.
Link Page Generator
An open source project written in Perl.
Link Scan
A Perl link checker for Unix and Windows.
Link Verify
An open source java tool.
Free Online Link Checker
Free online service which checks the links on a single page.

3. Nodeworks
An online link checking service.
Scriptol PHP Script
An open source PHP script.
Site Mapper
A website mapper for windows which also validates links.
SortSite
A Windows desktop application which Checks websites against various standards & checks links.
Web CEO
A Windows desktop SEO tool which also finds broken links.
Web Link Validator
A Windows desktop program which checks for broken links among other types of errors.
Xenu's Link Sleuth
Probably the most well known free desktop link checking application for Windows.