Sketch Mirror - Preview your iOS designs directly on your devices
IcoFX - IcoFX is an all-in-one solution for icon creation, extraction and editing.
Flowkit - Sketch library for user flows/content maps/annotations
IconsExtract - Extract icons and cursors stored in EXE, DLL, OCX, CPL files
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.
JDraw - Open Source SF.net