As @finnra mentioned, Anki is popular. I’m not personally a fan (I like someone telling me that I’m right or wrong instead of having to decide by myself). If you’re just looking to learn common vocab, there are a number of 2k, 6k, 10k decks with the most common words (as taken from Japanese newspapers, I believe). You can study those decks through Anki, or you can use Torii, which uses a similar SRS system as WaniKani to teach you the 10k vocab.
There’s also Kitsun.io which I haven’t used but I believe has similar 10k decks to study using SRS.
I personally keep track of every new word I come across while reading in a spreadsheet, and how often I come across it in different contexts (in other words, if it pops up 5 times in the same conversation, I only mark it once). If I encounter a word more than twice, I add it to my Houhou deck and use the SRS from there to learn the words. However, Houhou is Windows specific, so that might not work for everyone.