Sketch Mirror - Preview your iOS designs directly on your devices
Muzli - UI/UX and Design Inspiration Chrome Extension
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.
UI Garage - Specific mobile and web design patterns for your inspiration
Flowkit - Sketch library for user flows/content maps/annotations
Design Hunt - Curated design inspiration for everyone