Meazure - What are the dimensions of that image? How big is this window?
On-Screen Ruler - lightweight, free, semi-transparent ruler
Measure Schmeasure - Measure Schmeasure is a simple screen ruler for measuring the width or height between pixels in any...
JR Screen Ruler - JR Screen Ruler, also known as JRuler - Free virtual ruler for your computer screen.
Meander - Measuring tool and route planning software for mac OSX
Zeplin - Collaboration app for UI designers & frontend developers