My productivity app for the past 12 years has been a single .txt file
I use a single text file, have done this for decades. I dump everything into it and don't worry too much about structure, it's an incredible resource for "remembering" minutia, things like "what was that server that i thought might have had some issues last August?" Just a quick control-S and I'm there. My current 7+ year old notes file has about 100K lines in it right now. I can tell you what I was doing last year, or the year before, on this day, in seconds.I just type    note (maybe some text here)

and it cracks open Emacs on the notes file, adds a timestamp, appends the optional text, and then I can just type or paste something in. Nearly frictionless, that's key. Great for writing those miserable annual reviews, too (easy answers to "what have I worked on in the past year?")I use plain old notebooks (simple blank sketchpads, or something bound like a Moleskin/Lecchturm) for meetings, interviews, walking around datacenters and so forth where a keyboard is awkward and anyway, drawings.I've tried the EverNote/OneNote/etc. apps and none of them were as convenient or as easy to use, or as portable.