The cartridge slot on the DS was designed so gamers can play titles from the vast GBA library. Then Nintendo came up with the idea to use the slot for expansion packs like in Daigasso Band Brothers and for a rumble pack as seen in Metroid Prime Pinball. Just when you think every idea has been dreamed up Sega packages accessories disguised as GBA carts. Now you can carry around an extra DS game by putting it in a hollow cartridge. Or you can have a screen cleaner handy at all times. Those accessories might be useful, but the touch pen doesn’t look better than Nintendo’s tiny stylus.