- Bullet journal. It's not an artistic statement, it's a tool for productivity. No battery-life issues, works in full daylight, no software UI/UX issues, and is automatically archived annually.
- Index cards. I keep a small stash in the inside pocket of the BuJo, as well as elsewhere (home, office, tucked into my book bag). When inspiration strikes or information needs annotating, that gets recorded. Cards are filed in boxes (roughly 3,000 cards per box). Not as searchable as digital records, but the process of trawling through the archive itself is a powerful mnemonic.
- Tickler file / 43 folders. One for each day of the month (31 folders) 12 for the year (43). Works well with the index-card method given a dedicated card file box and 43 tabbed dividers. Manages recurring / planned future events. Can be fed by / to the two systems above.
- E-ink tablet. Used for reading books & articles and listening to podcasts. This is the natural digital successor to the PDA in my view, though it shares numerous failings of the latter: software-mediated, battery-life issues (though e-ink can provide far longer life than emissive displays, in practice when used for tasks other than strictly book-reading, it requires a daily charge, perhaps more). Though there are many apps for various tasks, these tend to be silos, are end-of-lifed with alarming frequency, and the entire platform is one huge privacy tarpit. That said, handwritten note-taking systems can be useful. They have worse search characteristics than index cards however.
- Note-taking / personal wiki such as emacs org-mode, vimwiki, ikiwiki, Mediawiki, etc. These offer powerful capabilities beyond pen-and-paper systems, though typically require at a minimum a laptop (or notebook) computer, preferably a desktop and/or server. Keep complex notes and concepts, synced amongst multiple systems. Inherent cross-referencing which is amazingly useful.
Actually, punched cards might be better. More bytes per card. Watch out for spillage though.
L'chaim!