xScope 4.4.1 MAS | Mac OS X | 29 MB. 

Created specifically for designers & developers, xScope is a powerful set of tools that are ideal for measuring, inspecting & testing on-screen graphics and layouts. xScope’s tools float above your desktop windows and can be accessed via a toolbar, menubar and/or hot keys.

The ten tools that will help you do your job faster and more accurately include:
• Mirror
• Text - New!
• Dimensions
• Rulers
• Overlay - New!
• Screens
• Loupe
• Guides
• Frames
• Crosshair

Compatibility: macOS 10.10 or later, 64bit
Mac App Store: https://geo.itunes.apple.com/app/id889428659