(Description by Simon Willison, which is more clear than the one on the site itself.)

Blake Watson's brand new HTML tutorial, presented as a free online book. This seems very modern and well thought-out to me. It focuses exclusively on HTML, skipping JavaScript entirely and teaching with Simple.css to avoid needing to dig into CSS while still producing sites that are pleasing to look at. It even touches on Web Components (described as Custom HTML tags) towards the end.

Github: https://github.com/blakewatson/htmlforpeople

License: BY-NC-SA 4.0