Sketch to App Store - Generate App Store images for all iPhone sizes from Sketch
Timeline for Sketch - Create beautiful timeline animations in Sketch
AppMockUp - Create the most compelling screenshots for your app.
Artboard Studio - Online graphic design app mainly focused on product mockups.
AppLaunchpad - Create free beautiful screenshots for App store/Google play
iOS 8 GUI for Sketch - A Sketch template of GUI elements found in iOS 8