It depends on the kind of notes: For information you want to retrieve easily later on: markdown files (avoid any wiki-like format that isn't widely used) + som

It depends on the kind of notes: For information you want to retrieve easily later on: markdown files (avoid any wiki-like format that isn't widely used) + some way to sync those files (e.g. unison, synching, Dropbox etc.). The app doesn't really matter but I use vim on my workstation, notebook, phone, tablet etc. For overviews, outlines, mind maps, notes in a meeting: a white sheet of paper. You can scan it, put keywords in the filename etc. I avoid tech in meetings. For sketches: a small notebook (A6 format) I always carry with me. At my age, it's more natural for me to think with a pen in my hand than with a keyboard below my fingers.