Why did you make it?
Who the heck can keep transistor package names straight? Sure the SOT names make a little bit of sense, but who can keep track of the difference between an SC-88 and an SC-88A? And wait is one of those also an SC-70-6? And what the heck are the TO sizes all about? I've been designing PCBs for almost 20 years and it's infuriating! Instead of shaking your fists and screaming "WHAT THE SOOOOOOOT???!?!?", grab this handy PCB ruler. Easily see at a glance alternate names for each package, and how big each footprint is in real life.
What makes it special?
Other PCB rulers have a few transistor patterns with maybe one or two common names, but this has every single darned one I could dig up. It is the ultimate transistor reference, every PCB designer or hobbyist who lays out circuit boards needs one!