Sketch Mirror - Preview your iOS designs directly on your devices
Mobbin - Latest mobile design patterns & elements library
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.
pttrns - iPhone and iPad user interface patterns
Flowkit - Sketch library for user flows/content maps/annotations
Page Flows - User flow design inspiration for mobile & desktop