DIRECT ANSWER
An Islamic app is software that serves Islamic practice or Islamic institutions: prayer, Quran, learning, community, and the administration behind them. What separates a real one from a reskinned template is engineering that respects the details: correct qibla computation, proper Hijri calendar handling, Arabic text that renders right, and content from verified sources.
How does an app compute the qibla direction?
The qibla is the great-circle bearing from the user's location to the Kaaba in Makkah, computed from two coordinate pairs with spherical trigonometry. The mathematics is short; the failure points are practical. Device compasses need calibration and drift near metal, magnetic north differs from true north by a declination the app must correct, and a phone held flat reads differently from one held upright. A qibla feature that skips declination correction points confidently in a wrong direction, which is worse than no qibla at all.
Why is the Hijri calendar hard to get right?
The Hijri calendar is lunar, and months begin with the sighting of the new moon, so no formula settles the date for every country. Tabular calculations (and the common astronomical variants) can differ by a day from a country's official announcement, and one day matters when it decides the start of Ramadan or Eid. A correct app treats the calculated Hijri date as a default, applies the user's regional adjustment, and follows official announcements where an authority publishes them. Hard-coding one conversion table ships a calendar that is periodically wrong everywhere except its author's country.
What does Arabic support actually require?
Arabic support means more than a font. The script is cursive and contextual: letters change shape by position, and Quranic text adds diacritics and symbols that many fonts render badly. Layout must flow right-to-left, and a bilingual app must mix RTL Arabic with LTR text without scrambling either. For Quranic content the bar is higher again: the text must come from a verified source, never retyped, because a rendering that drops one diacritic changes recitation. This is why Quran app development starts from verified text and audio sources rather than a database someone filled by hand.
Is a reskinned template app "Islamic"?
No. A template with a crescent icon that gets the qibla declination wrong, shows Eid a day off, and breaks Arabic ligatures serves Muslims worse than no app, because users trust it. The label "Islamic" is earned by the engineering above plus honest monetization, and users check: the reviews of every prayer app are full of people comparing its times against their mosque. Details on the time side are in prayer time calculation methods.