In the last six months I’ve learned over 500 kanji characters and Japanese vocabulary words using WaniKani, a “spaced repetition system” flashcard website. The first 3 levels are free, after that you can pay by the year or buy a lifetime account. (Disclosure, my wife used to work at WaniKani’s parent company). — MF
Dr. Moku’s Hiragana and Katakana apps use mnemonics to help you memorize the Japanese syllabaries. Within 60 minutes I had all the syllables memorized (roughly 100). — MF