Hacker News Reader

Not quite as old (circa 1978) but TeX is still alive and well: https://en.wikipedia.org/wiki/TeX

Moreover, TeX has no serious competition (at least in the niche of typesetting mathematical documents). There are plenty of good text editors and IDEs to go around.

What about groff?

How does groff do formulas?

Using separate programs like eqn. (http://www.kohala.com/start/troff/v7man/eqn/eqn2e.ps)

Sorry, but eqn is just not in the same league as LaTeX. It's okay for simple equations, but as can be seen from the document you linked, it produces awful output as soon as the equations become a little bit complex.

Take a look at http://download.savannah.gnu.org/releases/lout/lout-3.40-use... (page 148 and followings).

Lout (http://savannah.nongnu.org/projects/lout) and troff/groff (https://www.gnu.org/software/groff/). Both do equations quite well, I would even prefer lout (it is a way more comfortable than LaTeX), but the lack of additional packages makes it inferior. Troff is older than TeX (not sure how old is eq package).

Reply on news.ycombinator.com