Delphi developers can freely download the full Screen RULER source code (Delphi for WIN32 source).
Screen RULER provides (follow links to learn about the implementation) a transparent window, with no caption/title bar (that can be moved by dragging from inside forms client area) with stay on top option. Screen RULER is a great example of extending a form functionality (by overriding the CreateParams procedure). Position and options are stored to an INI file.
Screen RULER can be extended with new ideas; here are some you can add to the code: form/window skinning, non-rectangular appearance, measurement in other units (inches, picas, points, etc.), screen zooming, placement in System Tray, fancy popup menu, ruler background color, ticker color, etc.
Feel free and encouraged to add any of the new features to Screen RULER. Send me your version of Screen RULER, I'll be happy to make it available to others here.
If you need any help with the code, be sure to post your questions on the Delphi Programming Forum.