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
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.
SVGator - Online SVG Animation Creator - No Coding Skills Required
Smartmockups - Create stunning product mockups, easily and online.