From the website:

"CharacterPal is a widget that helps you remember how to type any special character. Just put your mouse over a character, and the key combo appears at the bottom. Now you don't have to remember what Option + Shift + K does."

"CharacterPal 4 allows you to help you use the widget on your Desktop. Just drag CharacterPal while closing Dashboard."

You could call this the descendant of "Key Caps", part of the Desktop Accessories on the original Macintosh.