Yeah, you can think of the Gateway as some sort of blank cart. http://www.gateway-3ds.com/
It is a homebrew and edited game enabler as well. With it, you can create a separated NAND partition (which allows you to run games at any firmware) and also allows any kind of game to run (which is important, because actual games require a valid signature that cannot be produced by anyone but Nintendo, and as soon as a game is edited, that signature becomes invalid.