A Real Validator: Windows. Based on an SGML parser. Shareware.
CSE HTML Validator: Windows. HTML, XHTML, and CSS validator. Also checks accessibility, links, and spelling. Commercial pro version and free lite version.
Demoroniser: Perl script which corrects incompatible HTML generated by Microsoft applications.
Firefox extension HTML Validator: A W3C Tidy-based HTML Validator which checks pages from within the Firefox web browser.
HTML Code Cleaner/Compressor: Windows. Optimizes HTML documents removing unnecessary HTML code while checking links. Commercial software with free trial.
HTML PowerTools: Windows. Includes validator, image scanner, meta tag manager, find and replace tool, tag pair fixer, and an HTML to text converter. Commercial software; 30-day demo.
HTML Shrinker: Windows. Removes unnecessary characters from HTML, CSS, Perl, JavaScript and many other web file formats. Commercial pro version and free light version.
HTML Tidy: Unix, Windows, MacOS, and others. Validator fixes errors in HTML and XHTML. Converts HTML to XHTML. Free Software.
LinkScan/QuickCheck: Unix and Windows. Lint and link checker. Commercial software; free trial. Also online checking.
SP: Windows and Unix. Object-oriented toolkit for SGML parsing and entity management. Can validate any version of HTML for which a DTD is available. Free Software.
SP Instructions: Windows. Instructions for the Do-it-yourself Offline HTML Validator using SP.
SWAN: SubWeb Analyzer: Unix. Generates statistics and finds inconistencies in a subweb (web site).
WebLight: Linux, Mac OS X, and Windows. Finds broken links, non-standard HTML, and links between URIs on web sites. Commercial software; free for small sites.