See the project page for details.
ScreenRuler was written some time ago as my first application for the GNOME desktop. Although I chose to make a ruler just to fill the gap (a screenruler existed for Windows, OSX and KDE), I’ve actually found it to be extremely useful, using it almost daily for GUI and website design.
It was recently rewritten in Ruby, reducing code size by 65% while also improving ruler rotation behavior, switching to Cairo for the rendering, and moving metric selection (inches, picas, etc.) from the preferences menu to the popup menu.
I’ve been really happy with my C -> Ruby rewrites so far. They are consistently smaller, easier to maintain, more fun to work on, and an end to compilation and packaging nightmares.