IconBox organizes icons into so called "Boxes", you can think of them as an iPhoto album. You import icons into them by drag-and-drop, or by choosing File > Import from the IconBox menu.
IconBox can import different formats: ICNS, PNG, TIFF, JPEG, GIF, PDF and even the iContainer format.
Don't like the look of your Photoshop icon, need a cooler World of Warcraft icon? This is the place to be.