XChar for Mac

From Angelo Scicolone:

XChar allows you to quickly use uncommon characters even if you don't remember the key combination you need to use a certain character. How? XChar displays a window containing all the characters that your Mac can display. When you need one of it, simply drag and drop it on the place where you need it. And when you don't need XChar, you can reduce its window to a small icon and place it where you want on your screen. When you'll need it again, simply click on it and it will zoom again. Moreover, XChar is a standalone application and doesn't need any special extension to run.