dsidl is a WIP tool for allowing simple downloading of files by scanning QR codes using the DSi's cameras. It supports WPA Wi-Fi security, but has issues with some Wi-Fi routers due to the dsiwifi library's compatibility issues.
Aim the camera at a QR code and select "Scan QR" in its menu or press the L or R buttons. Once it successfully reads a QR code it will ask where to save that file to, then download it. It supports simplistic JSON-based scripting in the QR codes to allow downloading multiple files from a single scan and specifying where to save to.