An adapter that allows you to plug an ordinary PS2 controller to the USB port on the back of your computer.
After I had moved a few months ago I somehow seemed to have lost both of my gamepads. This was very devastating, as playing an emulated Super Mario World on the keyboard was quite difficult. I decided to check on eBay for an adapter for my wonderful PS2 controllers and try to save some money, and get to use a great controller on my PC to boot. Low and behold, my search on eBay for "PS2 controller USB" came up with the:
I was a little nervous purchasing said product considering who knows with what sort of quality it was built with. I didn't want it shorting my USB bus or frying my somewhat pricy PS2 controller. I weighed the risks and snatched it up for around $8 including shipping. When it arrived 2 days later I anxiously unpacked my parcel and was quite unnerved as I read the "System Reguirtuments" on the back of the packaging. I plugged it in anyway. Within seconds, Windows XP detected "MP-8888" and I tested my new gamepad out under "Game Controllers" in the Control Panel. Everything seemed to work: all 12 buttons, both analog sticks, and control pad! I decided since its working so well I guess it wouldn't hurt to try to install the drivers that came with it on a floppy (a floppy!!!). I was plesently surprised that Force Feedback now worked!
You don't know what you've been missing until you've played Super Mario World on a DDR dance pad!
In doing a little research for this writeup it seems there are also "Super Joy Box" 4 and 5 for sale. SJB 4 allows two controllers to be connected to it, and SJB 5 allows four controllers!