It is a TCP server running on the Wii that listens on port 8080 and will run any binary that is sent to it after you confirmed the IP address with your GameCube controller. An additional warning is displayed when the connection comes from the Internet (i.e. the first two octets of your Wii's ip does not match the first two octets of the connector's ip). Both DOL and ELF executables are supported.
A working windows gui has been written by henke37 and dasda and is avalible from henke's site. The Wii server part is included. Henke asks that people don't go and rehosts the client, but adds that he does not mind hotlinking to the download.
You currently need libogc cvs to compile this yourself from the source code.
Download (linux binary and Wii server)
The client first sends the length of the file to load in big-endian int32 and then the data of the file. There is no traffic from the server.