This is an example of customized sticker pack for iMessage.
Sticker browser is implemented as UICollectionViewController with a custom layout.
This project can be used as a starter kit for creating new iMessage app. You can change only assets and background colors, or you can do something more advanced and change how the layout is organized.
This app is a part of the tutorial on iMessage sticker apps.
Screenshots of example projects, and other comercial project implemented with this approach are bellow:
