Hira2Kata was created to help you learn katakana characters in terms of the corresponding hiragana. The reference table is handy for figuring out what hiragana character(s) you need to type to get the katakana suggestion on the iPhone 12-key hiragana keyboard. The SRS page is a simplified version of the standard spaced repetition algorithm called SM-2. Your progress will be stored in the browser's local history.
All of Hira2Kata's functionality is also available in the Encanto Nihongo app, along with additional features like kana drawing practice.