Sketch Mirror - Preview your iOS designs directly on your devices
Hellosaurus - Interactive mobile shows kids can play, not just watch
Flowkit - Sketch library for user flows/content maps/annotations
Hullabalu - Interactive stories for kids
Crystal: Sketch Mirror for Android - Crystal: Sketch Mirror for Android is an application that is designed for viewing your sketch designs in real-time, navigate prototypes and download content related to the sketches for offline viewing.
Tellast - Write stories collaboratively with others