What exactly is it?

okay lemme see if i can explain this so that its legal.... okay technically your not supposed to download a cd unless you have the cd in your possession... basically the same thing here.. lets say you have a bunch of ds games in your collection you could download the ds roms and upload them to this device and have up to two gigs worth of games or however big your sd card is that you use i think the device my nephew has only supports 2 gigs... and he can put like 20 games on his ds.. so he doesn't have to carry around the cartriges... now you should be able to see what you can do with it... just like mp3s u can download reguardless if you have the game or not that up to you.. it is illegal but it'll save you money