Zhuyin (colloquially called bopomofo) was introduced in the 1910s as the first official phonetic system for transcribing Chinese, especially Mandarin.
The Bopomofo flash cards will help you to memorize the system.
There are 4 options in the App:
- Learning - where you can learn initials and finals,
- 3 testes: one, where you have to pick the sound of bopomofo, one, where you have to pick a bopomofo character, and mix test, where the option is random