From PreForm Assistive Technologies:
The PFiddle Collection is a growing collection of useful and pfun Macintosh software. Buy the collection once for $4.95 US, and enjoy any and all applications in the collection, now and in the future, without additional charge.
The second PFiddle in the PFiddlesoft Collection is Waccy Accy. Waccy Accy is a whacky accessibility game that is pfun for all users, including those with impaired vision. The more you play Waccy Accy, the more familiar you will become with where things are on your desktop.
To win Waccy Accy, reveal your full user name by flipping the placards displaying placeholders so they show their hidden characters. You are playing against the clock, and your best time will be recorded for posterity.
You can't type your name on the keyboard. Instead, move the mouse over text elements on the screen. The first matching character in the title of any eligible UI element counts. Don't waste time clicking it, though. As soon as you mouse over it, the corresponding placard flips to display that character. There are lots of catches that make this harder than it sounds, but there are also lots of cheats to balance the scales.