Sketch Repo - Collection of resources for anyone who uses Sketch
Sketch Mirror - Preview your iOS designs directly on your devices
Anima App - Design, get feedback, convert to code, publish, iterate.
Flowkit - Sketch library for user flows/content maps/annotations
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
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.