I’m not really planning to add features to this or enhance it in any significant way (mobile optimisation isn’t great, but it’s usable), but it exists now, so I figured I’d share it in case anyone finds it useful: http://angry4squigs.uguu.ca/
It’s exactly what it looks like and what it says in the footer: hiragana and katakana drills as quickly as you can type, with no polish whatsoever. It should only take a couple of minutes to go through the set each day, leaving only the characters you struggle with the most by the end of a week. It’s intentionally minimalist for people who like straight-forward pass/fail evaluations, but, as a result, it’s not very beginner-friendly, and there are far better tools readily available for people looking to learn kana from scratch (my sole reason for building it is filling in some gaps in katakana recognition).
All data is saved locally to your browser and the code is public-domain, so you can take it offline and feel free to repurpose it however you want, if it inspires you to build something fancier.
Its name comes from an ancient SWF video called Coin Bird and a friend who refers to Japanese as “squiggles”.