Depending on the complexity, there’s also abbrev-mode: https://www.gnu.org/software/emacs/manual/html_node/emacs/Abbrevs.html

There’s a fork of Openboard that is trying to update it, but AFAIK, it’s not published anywhere yet: https://github.com/Helium314/openboard

I wish this was exaggerated, but it isn’t at all. Every time I try to learn Haskell, I end up in some tutorial: “You know how you sometimes need to represent eigenvectors in an n-dimensional plane with isotonically theoretical pulsarfunctions? Haskell types make that easy!”