The mobile app industry is booming, with global revenue from app stores projected to hit $25 billion this year and $46 billion by 2016.

Top-grossing games are all free downloads that convince people to pay real money for in-game boosts. On top of the pile is Clash of Clans, which was earning $654,000 a day in February, helping maker Supercell to a $3 billion valuation.

There are other ways that apps make money too. There are paid apps, the highest-grossing of which is Minecraft — Pocket Edition, coming in 30th. And then there are also successful non-game apps, like Pandora, which offer an upgrade to a better service for a one-time or recurring in-app purchase. Apple typically gets a 30% cut of purchases made in its app store.

We've pulled together today's 15 highest-grossing games in Apple's App Store using data from App Annie and estimated average daily revenue and new daily users from Think Gaming. Think Gaming pulls together data from the past 18 months and updates its estimates on a daily basis.