It is a TCP server running on the Wii that listens on port 8080 by default that will run any binary that is sent to it. Both DOL and ELF executables are supported.
You currently need libogc cvs and bushing's socket patch in the sf.net patchtracker to compile this yourself. Precompiled binaries will maybe be released by me once this patch is in the cvs. Source code
The client first sends the length of the file to load and then the data of the file. There is no traffic from the server.