xScope for Mac

From IconFactory:

Created for designers by ARTIS Software & The Iconfactory, xScope is a powerful set of tools that are ideal for measuring, aligning and inspecting on-screen graphics and layouts.

xScope is six tools in one that will help any designer do their job faster and produce more accurate results:

• Rulers - On-screen rulers that measure distances and angles
• Screens - A dynamic view of smaller screen sizes and web browser content areas
• Loupe - A magnifying glass that gives you a close-up view of your work
• Guides - Markers for precise horizontal and vertical alignment
• Frames - Markers for precise width, height & origin alignment
• Crosshair - Finds the exact location on screen