[a_e_k]

It jumped out at me as a nice example of the Edward Tufte style (which I'm a big fan of -- I once published a tech report in that style). People have put together style sheets emulating it for LaTeX [1][2], CSS [3], and R Studio Markdown [4], among others.

[1] https://tufte-latex.github.io/tufte-latex/

[2] http://tug.ctan.org/tex-archive/macros/latex/contrib/tufte-l...

[3] https://edwardtufte.github.io/tufte-css/

[4] https://rstudio.github.io/tufte/

[Mageek]

The authors open-sourced their setup for Tufte-style books: https://github.com/sisl/tufte_algorithms_book