It's a Screen Ruler for Windows.I wrote this a while ago because I needed to measure something.
Changelog:
Changes in v1.3
* SPACE toggles Between vertical and horizontal.
* Added tooltip option that shows width and height.
Changes in v1.2
* Added keyboard nudging and resizing: Arrow keys move the ruler five Pixels, CTRL+ArrowKey moves it one pixel and CTRL+Shift+ArrowKey resizes it.
Changes in v1.1
* Added "Vertical" option.