Interesting idea, although I'm not sure of the choice of engines. I recognize LaTeX and groff, but none of the others. And conversely, engines that I would expect to be there like plain TeX, Lout, and even just Markdown (which combined with pandoc can be used to typeset documents). aren't there.
Is this “typesetting” only referring to things like page layout? For glyph rendering and shaping, I thought FreeType and HarfBuzz were the most popular open source engines, which I don’t see here.