It’s called Kanji Teacher. Just a basic flashcard app.
This website is way better though- it explains the context of the words and gives you examples of how they’re used. Pronunciations are only in hiragana though, so you’ll have to learn that first.
http://kanjicards.org/kanji-lists.html
Sometimes the first few lists seem like they contain a weird assortment of words, but that’s because those characters are basic ones that are used later as elements to build up more complicated words. Like 貝 (shellfish) seems a weird one to put in an elementary list, but it’s used in lots of words to do with money, buying and selling.