Lout (http://savannah.nongnu.org/projects/lout http://savannah.nongnu.org/projects/lout) and troff/groff (https://www.gnu.org/software/groff/ https://www.gnu.or

Lout (http://savannah.nongnu.org/projects/lout http://savannah.nongnu.org/projects/lout) and troff/groff (https://www.gnu.org/software/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).