This isn't the shiny, gold paint-plated cheat cart of the NES days, but it has the same name. Hyperkin's Game Genie for the DS does similar things, though. Through codes you'll have access to cheats like unlimited life, endless ammo and top stats tweaks. 300 DS titles have codes available.
This Game Genie is compatible with 3DS, DSi, DSi XL, DS Lite and DS, but only with DS games. Codes are being added to the device's webpage, and can be downloaded for use.
For $20, this thing is pretty decked out. It has a built-in MP3 player, and through the DS's Wi-Fi receiver permits upgrading. It even has a movie playback feature, usable by inserting a Micro SD card into its slot.
Pokemon cheats, anyone?