(All links are to the respective threads here on the forums.)
KameSame is a website that was originally created to reinforce stuff you’ve learned on WK by testing EN>JP, but it’s since expanded beyond that. They’ve got various lists you can do vocab lessons from, as well as a field where you can enter text and it’ll search for the vocab in the database and you can add those to lessons. It doesn’t test on JP>EN meaning like WK, but the reading and meaning cards are completely separate, so you don’t have to do them both. You’re also able to ignore any card, even after you’ve added it to your review queue. You get a limited number of undos, but if you donate, you unlock an option to toggle in settings that allows unlimited undos.
And then there were two that were applications you download onto your computer rather than websites. Houhou also functions as a dictionary, and it allows you to edit cards and even make your own if a word or phrase isn’t in its dictionary. Reviews look a lot like WK, but there’s no lessons, so no quiz before an item goes into the queue, which for me meant my retention was awful. I think the other one I gave a shot was Torii? I don’t remember anything about it though.
If you don’t care about it looking like WK, the big one of course is Anki, but I don’t remember any others I’ve heard people mention. But then there’s also BunPro. I don’t know if their vocab is still in beta (though any user can opt in in settings), but they have multiple input methods, including meaning and fill-in-the-blank (I think you can only have one per card, but I also think you can change it per card? unless it’s only per deck), and you can freely add and remove cards from lessons and also auto-burn them from the item page at any time. By connecting your WK account, you can also choose to auto-burn all vocab you’ve already encountered on WK. I think the only vocab they have though is JLPT and/or textbook vocab, though they do still have a ton of it. I haven’t exactly looked at vocab in a while, though.