Paid to use (with 14 days for free), but my favorite SRS platform.
There’s a couple of decks on this platform like the 4.5k katakana vocab deck, the Core 10k and the Genki vocab deck (the latter 2 have kana words in it which you can choose to study first). I also published a deck there called WK Expansion Pack, which has common vocab order by WK level that is not on Wanikani. Which means that as you go on leveling up on Wanikani, you can supplement with it.