I'm sure you all know what the Action Replay is but just for those who don't let me explain.  The Action Replay is a device that allows you to cheat on games by changing the program with the use of codes entered through the Action Replay.  Codes normally offer such extras as infinite items or energy or in some cases can open up locked levels of games.  These codes can be found in Magazines or on the net.  Or if you're skilled enough you can find your own codes by connecting your Saturn through the Action Replay to your PC via the parallel port in the to of the cartridge.

The Action Replay version shown here is the 2nd rendition.  Even though it says it's by Karat it is in fact by the British company Datel.  I guess Karat is just their Japanese label.