This is UML: http://en.wikipedia.org/wiki/Unified_Modeling_Language It's entirely possible (although tedious) to create these in html with css and divs. Sounds like more effort than it is worth, honestly. If you have a UML editor, why not just export to a web format like jpg, gif or png and move along?
I found this page with a nice list of freeware UML tools, but I'm not sure when it was last updated. It might be a good place to start though.