Kanji Damage is a website where you can learn 1,700 kanji for free with mnemonics, and is known for its unapologetically casual writing style. Maybe a little too casual (and even a little offensive) for some people. Kanji Damage is extreme, but compared to other resources' traditional academic voice, you might find it more entertaining or approachable.
Overall, the content is definitely NSFW, but if you don't mind that kind of language, Kanji Damage is a decent option you can use for free. The program itself is designed from a learner's perspective, and offers hints to help users tell apart kanji that look alike. And on each kanji page, you will see a list of vocabulary that uses the kanji as well so that you can see the kanji in context. Each kanji compound word (jukugo) shows how it is made out of different kanji components and how it got its meaning from them, making it easy for you to piece them together and remember.
Although Kanji Damage is a website, note that it is NOT an interactive tool. It is a collection of plain web pages, and in fact, the author actually calls it a "book." So, it won't save your progress, and you won't be able to review or practice with digital flashcards that are built-in, like WaniKani does. However, you should note Kanji Damage has an official Anki deck, so even though it's not built-in, you can use that as a tool to review what you learned on Kanji Damage.
Lastly, their 1,700 kanji coverage is a few hundred short compared to what similar kanji learning programs cover. The author used a list of kanji from JLPT and jōyō kanji, then "threw out all the bullshit ones," using their judgment of what's useful and what's not. While most of the excluded jōyō kanji are indeed obscure, it's definitely on the fewer side as a complete kanji learning program.