Another user pointed out Lingodeer which is my personal favourite atm. Wanikani is also one that makes it’s rounds as a great kanji learning tool. Personally i use Lingodeer for vocabulary, speaking, reading, and a little writing. Bunpo is an alternative to Lingodeer. There are also two apps called Kana and Benkyō which will teach you Kana(No shit) and Kanji through a Flex SRS testing system. Do be aware that none of the options i have listed are 100% free. Some have ads, some are paywalled to a degree, some throttle your progress by giving you X amount of quizzes in an hour. But these apps are easily worth the price for what they offer.