A client for sb_xmlrpcserver.py.
Just feed it your mail on stdin, and it spits out the same message with the spambayes score in a new X-Spambayes-Disposition header.
The full documentation for sb_client is maintained as a Texinfo manual. If the info and sb_client programs are properly installed at your site, the command
info sb_client
should give you access to the complete manual.