The مكتبة كتب أصول الدين app is an Android application developed by So Smart Apps. It is a free app that falls under the Education & Reference category and specifically the Books subcategory. The app provides a collection of Islamic books on the fundamentals of religion. The books are sourced from المكتبة الشاملة الذهبية.

The app contains several books, including "40 Questions on the Fundamentals of Religion" by Abu Abdullah Muhammad Bin Khalil Al-Sakouni Al-Maliki Al-Ash'ari and "Islamic Fundamentals and its Four Principles" by Muhammad Bin Abdul Wahhab Bin Sulaiman Al-Tamimi Al-Najdi. The books cover various topics on Islamic principles and beliefs. The app is designed to provide users with an easy-to-use interface to access these books.