Hisnul Muslim, also known as The Fortress of the Muslim, is the most well-known Islamic prayer book in the world. It is a small reference book of supplications for various occasions derived from Quranic verses and authentic narrations of the Prophet Muhammad, peace and blessings be upon him. The book was compiled by Dr. Sa'id ibn Ali ibn Wahf Al-Qahtani and is a project of the House of Islam and Jugend für Deutschland.

The app features a simple and easy-to-use interface designed by Omar Wels, enabling users to navigate and find the desired supplication easily. It also allows users to bookmark their favorite supplications for quick access. The app is available for free on Android devices and is a must-have for Muslims who want to memorize and recite supplications daily.