LaTeX is an amazing typesetting language that I mostly use to markup various mathematical formulas. I am currently learning more about it and try to use it here in the wiki too with KaTex plugin.
Mathpix - Take a screenshot of math and paste the LaTeX into your editor, all with a single keyboard shortcut.
PlotNeuralNet - LaTeX code for making neural networks diagrams.
Tips and Tricks for Writing Scientific Papers - Best practice and tips & tricks to write scientific papers in LaTeX, with figures generated in Python or Matlab.
Engrafo - Convert LaTeX documents into beautiful responsive web pages using LaTeXML.
LaTeX3 Development Repository - Contains development material for LaTeX3.
Eisvogel - Clean pandoc LaTeX template to convert your markdown files to PDF or LaTeX.