On-Screen Ruler - lightweight, free, semi-transparent ruler
Fileion - Fileion is a software-related website where you can download and get reviews software.
Bluegrams Screen Ruler - A lightweight and configurable ruler tool for Windows Desktop.
Downzen - Downzen.com provides comprehensive reviews and downloads for software in an easy and reliable way.
Pixus - Pixus is an AIR pixel ruler application, a handy tool for web and interface designers.
IceWalkers - IceWalkers.com provides a vast database of Linux Software.