AC Diary is an iPhone application developed by NIPPON INFORMATION CO.LTD., available for free in the Education & Reference category. This app allows users to create multiple diaries tailored to different themes or subjects. Users can customize diary covers with various colors, orientations, and cover images, enabling the creation of unique and personalized diaries.

The app features folder categorization for organizing diaries efficiently. Users can record their entries using handwriting, text, photos/videos, items, and audio. Various customization options such as different background styles, pen types, masking tape for decoration, and eraser function are available for a personalized diary experience.