Nintendo e-Reader

The e-Reader is a device made by Nintendo. When plugged into a Game Boy Advance, it can scan cards, which have specially encoded data printed on them, to perform various functions, such as play a game or interact with another game.

Use in Animal Crossing
When the e-Reader and Game Boy Advance are connected to a Nintendo GameCube playing, cards from the Animal Crossing-e series can be used to affect gameplay, including unlocking rare NES games.