I use org-mode heavily. I write specifications in it with ascii diagrams, code samples, figure captions, footnotes, etc... and export it all to a nicely fomatte

I use org-mode heavily. I write specifications in it with ascii diagrams, code samples, figure captions, footnotes, etc... and export it all to a nicely fomatted PDF with rendered diagrams (thanks to the bundled ditaa). I use it for organizing todo lists, time tracking, and generating time sheets. I've used it to publish a book. I use it as a super-powered Jupyter-style notebook for data analysis. It as a sub-package called org-babel that lets me interact with any language using the normal Emacs modes and tooling. This lets me query results from a database, send it to a code-block in my org file which executes on my machine and spits the results back into my org-file as a nicely formatted table. org-mode also has fully fleshed out spreadsheet system. For hacky analysis projects I can't think of anything better. I use it as a light-weight Kanban board/issue manager for personal projects as well.