The Gamester 3 in 1 for Gameboy Advance SP by Radica/Mattel

Edited for time. =) This device attaches to the GBA SP cartridge slot making it easier to play games without swapping carts individually making it a multi game player. It has a switch on the side to pick which game you want to play (note: the GBA SP must be turned off when you select.). A nice little peripheral to take with you albeit it makes your GBA SP bulky but great if you have big hands. Sorry about repeating myself. I made this video really early in the morning and I was tired.