KanaSensei is a web app for learning to read Japanese. Practice hiragana and katakana with adaptive drills, challenges, memorable mnemonics, native audio, and progress tracking.
I've tried a few kana apps before a trip to Japan and always dropped off after the first week because they either gamify it into a completely different activity or just throw flashcards at you with no hook to make a character stick. the picture-story mnemonic per character is the thing I actually needed - turning "つ" into something visual instead of just repeating it hoping it sinks in eventually. typing the reading instead of just tapping multiple choice also forces actual recall instead of pattern-matching against the options.
What needs improvement
would like to see katakana lookalike pairs (shi/tsu, ki/ka, so/n) drilled against each other deliberately instead of mostly one character at a time - that's where I've personally slipped up after having each character down cold in isolation.
Kanaquiz is a solid pure drill tool if you already have some retention strategy of your own, but it doesn't give you the mnemonic hook to build that retention in the first place - it assumes you already remember the character and just tests you on it.