GameCube EXI-to-USB Adapter
From Rare Gaming Dump
The GameCube EXI-to-USB Adapter (officially known just as the "USB-ADAPTER") is used for debugging GameCube and Wii software. The adapter has an end which plugs into the GameCube/Wii's EXI bus via the memory card slot, which then allows for a USB cable to be plugged in which can interface with special PC software to provide debug functionality.
The homebrew community has produced multiple recreations of this device under the name "USB Gecko" and later "Shuriken USB", however they are no longer in production and are now difficult and expensive to find due to a shortage of parts.