Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Meazure - What are the dimensions of that image? How big is this window?
Invision - Prototyping and collaboration for design teams
ScreenRuler - ScreenRuler lets you measure objects on your Ubuntu desktop using six different metrics.
Sketch - Professional digital design for Mac.
Bluegrams Screen Ruler - A lightweight and configurable ruler tool for Windows Desktop.