For simple stuff, I prefer org-mode. I have great memories of using OmniOutliner on OS X Tiger. The hierarchical nature of outliners is great for structuring th

For simple stuff, I prefer org-mode. I have great memories of using OmniOutliner on OS X Tiger. The hierarchical nature of outliners is great for structuring thoughts quickly. Org is even better, as it's plain text and has tons of modules for all sorts of crazy things, including kanban or spaced-repetition. And plenty of export options, including many facilitated by pandoc, literate programming, etc. I do use LaTeX, but I have a love-hate relationship with it. Lots of LaTeX packages don't compose well, and there are tons of pitfalls. But there are beautiful parts too, like TikZ or Memoir. I'd be happier with TeX, but few people use that.