My productivity app is a never-ending .txt file (2020)

Personally, I just use obsidian notes. Its simple enough, uses markdown, syncs to my phone. I like to break projects/problems out into checklists. Helps keep me motivated.

I don't use the 'linking' feature between notes. The whole 'second brain' thing seems like something you do to make a neat screenshot of your note graph. I just use regular old folders like a file directory. My notes have gotten a little messy though.

The nice thing about linking is that you can embrace the chaos a bit and not need to have everything organized into folders.

Transclusions (embeds) are very useful also.

I agree that the note graph visualizer is just a gimmick though.