I have a git repo with notes on all the things I'm interested in, a few larger files (some books I always reference, some images etc.).

Over time I've built up some scripts to help with general tasks, eg list TODOs etc.. It's perfectly moulded to my needs. For example, when I find a new utility I run mk_notes.sh [thing], which sets up three files:

  - links (for relevant web links)
  - thing.txt (which has basic info about it)
  - cheat_sheet.txt (which has quick useful things I want to keep)

These files suffice for the majority of cases. I used to have more, but found that was over-engineered.

I'm not sure I could buy such a thing, and if I did, I'd get irritated with some aspect of it sooner or later.

Search is easy (grep et al), git means it's available everywhere (for me).

It's literally changed my life, since I now don't 'lose' any research, and can pick up threads later and build.