A homebrew application for using your GBA as GameCube controller. Originally from https://github.com/CapitaineBidouille/gba-as-controller, but the repository is not available anymore. This file is the latest build provided before it went down.
Thread about the application: https://gbatemp.net/threads/gba-as-gamecube-controller.539048/
Thread about the application: https://gbatemp.net/threads/gba-as-gamecube-controller.539048/