The Wii Zapper is an accessory for the Wii, released in November of 2007 in the US. The Zapper is a plastic shell that holds the Remote and Nunchuck in a submachine gun-like configuration and adds a more gun-like trigger on the front grip.
The best feature of this accessory is its amazing sturdiness. The Zapper is very solidly built, and feels nearly impossible to break. It is also very well designed in that there are almost no extraneous cords swinging about: everything is very neatly wrapped up inside the body.
The one downside to this controller is that it can be somewhat uncomfortable to hold for long periods of time. The location of the trigger on the front grip feels a bit awkward, and the entire shell can be cramping for someone with large hands. However, it really does feel great in shorter periods, but it's only worth picking up if you're interested in light gun games or other shooters.