More and more, I'm starting to rely on Spaced-Repetition systems (SRS) for learning. That's WaniKani for Japanese Kanji and Vocab, Memrise for good courses they have (like the one on Morse Code) and Anki for everything else I want to remember, like Spanish Vocab, books I've read, Latin expressions or the Nato phonetic alphabet. Once I've mastered a course, it will also be migrated to Anki for maintenance.
At the moment, I'm only have thousands of cards, but I'm quite curious how long-term maintenance is going to work once I reach tens of thousands and more. For one, reaching a sustainable pace (say, 200 reviews a day) on a moderate set (10k cards, that's just the top 5000 words for a single language) will mean reviewing each card at most every 50 days.
I'm also trying to record random facts that I want to remember in Anki, essentially externalizing my memory a bit, but actually ensuring that everything that I want to remember longterm actually stays in my memory.
It will also be interesting to see if there's a limit to what I can remember. Is it 100k cards? A million? I will come back in a year and review my progress.