AWBot is an easy to use tool to test a web site. AWbot connects to your web site and make URL requests like any other visitors.
CheckURL is a tool to automatically check the content of URLs and send back notifications of changes in them by mail.
Checky Toolbar is a simple Interface for Web Content and Web Resource Developers to free and commercial Validator and Checker Services on the Web.
Flinch is a powerful and flexible web link checker that will make your life as a web designer or web server admin easier.
gmuck assists you in generating valid (X)HTML by examining the source code that generates it. It is not a replacement for real validation tools, but is handy in quick checks and in situations where validation of the actual markup is troublesome.
With LinkChecker you can check your HTML documents for broken links.
(commercial) LinkScan is an industrial-strength link checking and website management tool. The LinkScan" family of products delivers flexible test automation capabilities for the entire spectrum of web based applications.
Open Validator verifies and corrects many aspects of conformance of Web sites to standards of Internet best practices such as W3C WCAG and ISO/IEC 23026:2006 - Software Engineering - Recommended Practice for the Internet - Web Site Engineering, Web Site Management, and Web Site Life Cycle
PowerForms is a tool for extending your HTML pages with client-side input validation without requiring programming.
Pungo Spell is a PHP / DHTML Spell Checker. Requires Pspell, PHP 4.3.1+, NuSoap, and a modern web browser.
RailsTidy is a plugin for Ruby On Rails. It allows you to validate your rhtml templates, validate the HTML output of your functional tests, and clean up the HTML generated by Rails. It uses Tidy, the popular HTML validator and RubyTidy, Ruby bindings for Tidy.
Spike PHPCheckstyle is an open-source tool that helps PHP programmers adhere to certain coding conventions. The tool checks the input PHP source code and reports any deviations from adopted coding convention. It is essentially Checkstyle for PHP applications.
SWEC is a program that automates testing of dynamic Web sites. It parses each HTML file it finds for links, and if those links are within the site specified, it will check that page as well.
Tidybot is a cross-platform batch (X)HTML syntax-checker and report-generator. It traverses a directory tree of (X)HTML files on your hard disk, and generates a web page listing all the errors and warnings it encounters.
Web Based Open Source SpellChecker: designed to work with any text input form on any web page
Webalizer Xtended is an extension of Webalizer, which adds additional monthly statistics for all "404 Not Found" errors found in your server log-file, including the number of the "404 Not Found" requests and the corresponding 404 URLs.
WebVal is a system that will scan documents for fully-qualified HTTP URLs, keeping its database fresh with newly-seen URLs. It can then be requested to validate the URLs, whereby it will attempt to access each URL via an HTTP request and record the response code.