Behind the Epic-Apple trial is a booming app market worth fighting over

If there is one thing Epic Games Inc. and Apple Inc. can both agree on even as they battle each other, it is that the app economy is worth fighting over.

In the 13 years since Apple launched its App Store, the number of apps has exploded. The business of delivering them to people’s smartphones has grown into a revenue stream worth tens of billions of dollars annually for Apple and the other main marketplace operator, Alphabet Inc.’s Google.

App stores have become critical gatekeepers in accessing software that lets users do everything on the internet, including watch television, read books and check the weather.