The CD Stomper is an implement for properly centering and applying CD labels.
The Stomper consists of a round plastic base, with a spring-loaded center holder for the disc.
To use a CD Stomper, one peels the label from the sheet it came on, and places it around the center tower on the base, with the sticky side up. The disc is then placed, label-side down, on the center tower, and pressed down onto the label. The center tower guides the disc down into place so the label is applied right on center.
There are various other imitations of the CD Stomper around, and they all seem to work just about equally well. One variety even comes with newer Hewlett-Packard CD burners (good luck on assembly, as it comes in several pieces, and there are no instructions on how to get the silly thing together). If used properly, there's just about no way to get the label on off-center, which can cause noise or read errors when the disc is read on a high-speed CD-ROM or DVD-ROM drive.