Another HTML-Lint is another HTML checker written in Perl.  This package
includes individual command and CGI gateway.  Invoking htmllint without any
argument puts the usage string.

It supports various HTML versions and variants.  From usage string:

HTML1.0, HTML2.0, HTML2.x, HTML+, HTML3.0, HTML3.2, HTML4.0 Strict,
HTML4.0 Transitional, HTML4.0 Frameset, HTML4.0 Mobile, HTML4.01 Strict,
HTML4.01 Transitional, HTML4.01-frameset, XHTML1.0 Strict, XHTML1.0
Transitional, XHTML1.0 Frameset, XHTML1.1, XHTML Basic, ISO/IEC 15545,
Netscape Navigator (2.0, 3.0, 4.0), Microsoft Internet Explorer (3.0
beta, 3.0, 4.0, 5.0, 5.5), IBM WebExplorer 1.1, Compact HTML, NTT DoCoMo
iMode (1.0, 2.0), J-SkyWeb, J-SkyWeb Station, TTNet dot-i, HTML variant
for patent application in Japan

Homepage:
http://openlab.ring.gr.jp/k16/htmllint/
