Tuften is a theme for Tiki Wiki CMS Groupware based on Tufte CSS. Tufte CSS provides tools to style web articles using the ideas demonstrated by Edward Tufte's books and handouts. Tufte's style is known for its simplicity, extensive use of sidenotes, tight integration of graphics with text, and carefully chosen typography.
This theme would be appropriate for websites that are text- and idea-heavy or otherwise feature annotated text. The "sidenotes" are supported with Tiki's standard footnote plugin. I haven't tested with anything but basic footnote configurations, that is, no nested footnotes, etc.
The narrower text column is activated when the page is assigned to the "sidenotes" category. Then the page gets that category name as a class on the body tag, which is used for the CSS rule for the content column width and other details.
The page colors and typography are quite nice to work with and read; I could imagine adding some details in complementary colors to make a pretty nice magazine-style website with a not so scholarly look.