I unfortunately discovered Anki after graduating from uni (how I wish I had known about it back then). As a student of life I’m studying/maintaining the languages I speak, as well as general knowledge including geography and light history, plus anything new I’ve learnt and wish to remember.
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Irish traditional tunes.
I once studied some acoustic guitar tunes (before I ran out of interest).
Chinese (self-made, just adding words as I go), geography (The Ultimate Geography deck, plus customized decks for US, Canadian, and Australian political geography), the NATO phonetic alphabet (self-made), the periodic table (self-made + shared), and US Presidents (self made + shared).
I don't plan to add any more for a while because between Chinese, Geography, and the periodic table it's 40+ minutes a day already - but once the geography and periodic table decks have run out of new cards and settled into a dozen or so a day I might look for or create a nice piano deck. Maybe some more geography related ones as well.