AssetCatalogGenerator

AssetCatalogGenerator allows you to create app icons and image sets. The program accepts virtually any kind of image that is supported by OS X.

To create a universal iOS 8 app, you need to provide icons in 19 different sizes, as well as splash screens in 20 dimensions. For a modern OS X app you need to provide icons in 10 different sizes. It can be rather tedious and time-consuming to create these files manually.