Facebook Design - Devices - Images and Sketch files of popular devices.
Greenshot - Greenshot is a free and open source screenshot tool that allows annotation and highlighting using the built-in image editor.
Clay Mockups - Free set of beautiful device mockups for your designs
Shutter - Shutter is a feature-rich screenshot program.
Device Shots - Generate high-resolution device mockups using a screenshot.
Snipping Tool - Use Snipping Tool to capture a screen shot, or snip, of any object on your screen, and then annotate, save, or share the image