HIRAGANA Memory Hint and KATAKANA Memory Hint are mobile apps to help you learn kana with memory hints (aka mnemonics). Developed by The Japan Foundation Japanese-Language Institute, Kansai, both apps are available for free. The apps are divided into two parts: Memory Hints and Quiz.
The memory hints are overall helpful and intuitive, and they all come with cute illustrations. If anything, the unique art style makes it a bit hard to recognize the original characters in the illustration. Many of the illustrations sort of modify the shapes to make sense of the visual mnemonics (or at least, many look a lot different from generic font text). So if you ever use these apps, keep that in mind, and make sure to compare the illustration to what the character actually looks like. There are a couple options in the app that help you with this; one to see the mnemonic illustration and the original side by side, and another to play an animation of the illustration gradually fading out and the original character appearing after that.
If you go to the Quiz screen, there are four types of quizzes you can select from. In addition to the typical practice of choosing the corresponding romaji reading for each kana, the options include Listen & Choose, where you hear a sound and choose a corresponding kana out of three choices, and Similar Hiragana / Similar Katakana, where you see a sound written in romaji and choose a corresponding character out of two or three kana options that look alike, such as あ, め, and ぬ.
Another nice thing about the quiz feature is that you can narrow down the characters you want to practice by selecting a group(s) of kana. Each group contains two kana rows of eight to ten characters. Not many people cram all the kana in one sitting, so it's nice to be able to select and practice the kana you just became familiar with, before moving forward to study more.
However, it's worth noting these quizzes are all in multiple-choice format. Compared to typing or writing, it's a less strict method of testing your knowledge, or practicing your recall. But if you prefer easing into kana with a more relaxed approach, this could be a good option. Regardless of your answer being correct or not, you'll be shown the mnemonic illustration of the answer right after you answer each question. It's a nice gesture for people who had a hard time recalling most of the characters, but this feels redundant when you try to get through the session as quickly as possible or when you're already confident and don't need to see them. Quiz sessions are timed to motivate people to go through quickly, so being shown the mnemonic image can feel extraneous.
Overall, despite minor details that you may wish to change, HIRAGANA/KATAKANA Memory Hint is a legitimate option to learn kana with the help of mnemonics. And it's free!
As a side note… As of reviewing the apps (February, 2023), the audio was unfortunately not working at all on my iPhone 13 mini. Audio play buttons to check the pronunciation of each character doesn't work, and the Listen & Choose quiz doesn't play the audio either.