I haven't heard of the leo editor. I have used org mode in Emacs for little things. I also came across a reimplmentation of the tangling functionality: https://github.com/thblt/org-babel-tangle.py
It's worth playing with: it's primarily designed for writing literate Python, and I greatly enjoyed working with it on a project as an experiment. I shuttle between neovim, emacs and leo, and dream of an editor that would somehow bring together all of their benefits. Oh, and maybe some smalltalk too!