TeX
All I can say about TeX is this:
Knuth says that TeX is for producing beautiful documents, and he went to great lengths to build in a lot of typographic know-how. The hyphenation algorithm alone was the subject of a PhD thesis.
I credit LaTeX for my excellent grades as a senior in college. My writing hadn’t improved that much — ’twas all the text formatting. Great beautiful margin, footnotes like God meant them to be, mathematical equations Euler would kill for: LaTeX is where it’s at.