I use EVERNOTE as a file folder for storing client notes and some archived personal notes (how to install software and passwords on a new iPad or computer; miscellaneous current active notes or to-read notes). If you've never seen it, it's darn close to an Outlook email system (except it's notes, not email) with a list of folders and subfolders on the left, and showing each item (equivalent to teach email) by title on the right. It's been around for a decade so it's venerable.
I cycle around various To Do List apps, including paper notebooks, currently using ZENKIT because it lets me display and filter KanBan card columns by either category (Today, Tomorrow, Blog Ideas, etc) or Client (Ford, Toyota, Suburu, etc).
I ran across a new notes library complex app called AMPLENOTE which seems to have a lot going for it, and an entry subscription of $5 a month. Here. See a review (among 20 similar apps!) at NoteApps.Info here, here.
Regardless of the value and features of AMPLENOTE, they've got two interesting blogs on why To Do lists fail. Including the terminology "barnacle to-do" - after you use any To Do app for a month, you've accumulated an embarrassing several dozen unfinished to-do's that seemed like a good idea at the time you logged them.
https://www.amplenote.com/classic_todo_lists_always_fail
https://www.amplenote.com/blog/brush_off_the_barnacles
