Arguably I've spent too many months on this detail, but in addition to the standard DOM iteration, Unclutter uses a CSSOM iteration, patching of mobile styles, CSS word blocklists, and crowdsourced element selectors. Plus an animation system to move text to its "uncluttered" position.

Also interesting might be the article "library", a lightweight read-it-later list. It uses screenshots instead of titles & thumbnails, and drag & drop to move articles around. And there's an integration with Hacker News, where every top-level comment with an article quote in it automatically gets converted into an annotation.