It wasn't easy finding those pre-compiled open source binaries for HTMLdoc. I found again where I got mine. Works the same that I can tell as the commercial version, only the graphical interfaces says "open source" instead of "commercial version".
http://users.tpg.com.au/naffall/htmldoc.html
Click the "HTMLDoc1.8.24.zip" link. I think you'll need to execute (double click) the "HtmlDoc.reg" file to regeister the app with windows. You may also need to edit that .reg file for the path you unzipped this download to. Follow the instructions on the website above.