I use an app to take notes, tree-organised, on my mobile devices. Started in 2001 with Palm, from 2003 with Windows Mobile, from 2013 with Android. In the last move seven years ago I developed my app, since I didn't find anything adequate. In the years I developed it to suit all my needs: text input facilitation (it's WYSIWYG of course), advanced search, internal links, encryption, automatic calculations including spreadsheets, image editor, tasks, progressive backups... This is the beauty of make your own app. Encrypted files are sync daily on multiple devices. Recently, reviewing it for an Android, iOS and Windows implementation refresh, I had a look at other solutions out there - including DokuWiki, OneNote and Obsidian - but I found them too cumbersome, slow and limited. My main notes files, the personal and current work notes, have about 1,600 nodes/pages each. My oldest notes are from 2001. My job is knowledge and I do not have a good memory, so...