> httrack <http://www.example.com/> -O "example"
> "+*.example.com/*" -v -i
> I don't know how to restrict it to HTML though.

The problem is that httrack only allows to filter based on link names, nit
really on the MIME type, because it would require to check every single
links.

In your case, I would probably try something like!

-* +*.example.com/*/ +*.example.com/*/*.html +*.example.com/*/*.php
+*.example.com/*/*.htm

(assuming links ending with / or .html etc. are html)