Books such as Quantum Field Theory for the Gifted Amateur and The Visual Display of Quantitative Information use the margin of a book for displaying references, 'footnotes' and ancilliary information without interupting the flow of the main text. In addition, the use of a wide margin means that the text width is kept nicely short even on large pages such as A4.
sidearticle.cls is a very basic LaTeX document class, built on article, that uses these ideas to produce an appealing-looking article with good use of the margin.
This is acheived mainly through the use of the sidenotes and fontspec packages. As such, a modern typesetting engine such as LuaLaTeX or XeLaTeX should be used for building.
By default, the typefaces Minion Pro, DejaVu Sans Mono, Myriad Pro and XITS Math are used.