Execute code snippets, generate graphs from code, plot ... err... your plots. -- With a client/editor extension to do the character offset calculation for you, you can put the cursor into a code block, invoke md-babel on it, and get the computation result inlined into the document. Not side-effect free: if you configure plantuml or Mermaid for this, it will generate image files for you. Repeat calls will update the result.
The weirdest thing was when I ran Dwarf Fortress Adventurer Mode in text-output in Emacs and fiddled with custom key-bindings. (I still think there's potential, esp. for macros :))
The best thing is very boring, but it's the best because I use it all day, every day, and it brings me joy: bringing all my text things to Emacs. Writing, project/task organizing, and email. Never thought I'd end up there.
I think failing to some extent is fine, if the feedback is good and the device returns to a clean state. Even on a phone with buttons, she sometimes fat-fingers the wrong button super close to the phone-book-down key and ends up in the main menu, scrolls down 10x, then tries to hit the dial button for e.g. display settings. Phone appears broken because it just doesn't dial, and neither resets itself for invalid input so she could start over. She has no mental map of the various other states the phone might be in, and in confusion forgets that the hang-up button also returns to the home screen. Things are less than ideal.
She had a Windows Phone for years because you could zoom-in the tiles and thus increase touch targets for quick dialing. That eventually broke down, too, because of lack of haptic feedback and, well, we all can hardly imagine how hard it is to navigate a device like that when everything's so blurry you cannot see the space between huge-ass tiles on a, what, 6" screen or so.
