瘋狂背日語 - JLPT is a free Android app developed by CT Tseng that helps users learn Japanese vocabulary. The app includes over 8,000 commonly used JLPT (Japanese Language Proficiency Test) vocabulary words, which appear as pop-up flashcards on the user's phone screen at regular intervals. The flashcards automatically disappear so as not to interfere with the user's phone usage.

The app has several features including a floating window with the Japanese vocabulary flashcards, a toolbar for pronunciation, word translation, and word storage, a personal vocabulary library, customizable floating window settings, a Japanese online dictionary, and a self-testing feature. The app has received positive reviews from various professional app magazines, including Kocpc.com.tw and Briian.com.

Note: Users who encounter issues with word pronunciation can download the official Google pronunciation pack for assistance.