With projects like these, I’m always torn between thinking that it’s cool it’s possible, and horror that someone somewhere will try to use this in production code.

The only one I really remember is Trogdor, but in order to keep it in my heart, I am a proud owner of Trogdor!!: The Boardgame

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