AppMockUp - Create the most compelling screenshots for your app.
Sketch to App Store - Generate App Store images for all iPhone sizes from Sketch
AppLaunchpad - Create free beautiful screenshots for App store/Google play
DaVinci Apps - Сreate customized screenshots for your app in just 3 steps
iOS 8 GUI for Sketch - A Sketch template of GUI elements found in iOS 8
Screen - Seamlessly manage the electronic devices your family uses