Apple has shut down the iOS version of f.lux, reportedly arguing that the brightness management app violated terms of the Developer Program agreement.
An Apple representative, Richard Chipman, told f.lux co-founder Michael Herf that he wasn't allowed to turn either Xcode or the iOS SDK to f.lux's purpose, Re/code explained. The app uses private APIs, which are strictly banned at the App Store -- to get around this, however, Herf and his wife let people sideload the app for free via Xcode.
"The last six months of 'sideload' press -- which Apple didn't try to stop -- had convinced us that Apple would be receptive to an approach like this, but they seem to disagree," Herf commented. "I asked [Chipman] about open source used in a similar way, and he did not answer clearly, but he kept repeating the party line that we should make apps that could use public APIs."
While apps like f.lux are relatively unrestricted on platforms like OS X, Windows, and Android, Apple severely limits the reach iOS apps can have. Some software and hardware functions are completely off-limits, not only for the sake of security but also because Apple prefers to maintain control over the essential look and feel of its mobile devices.
F.lux first came to iOS in 2011, but only for jailbroken devices. Apple's began allowing sideloading apps through Xcode 7 earlier this year, in theory offering a more "legitimate" distribution option.