The "Obtaining the sources" of the programmers guide says you can download byteman from http://www.jboss.org/byteman/downloads. That is correct, but the link's href points to http://www.jboss.org/byteman/ instead.

That section also say you can get the source from svn at http://anonsvn.jboss.org/repos/byteman/. Byteman now lives on github, so it should probably be changed to point there.

The "Building Byteman from the sources" section documents an ant build, however byteman now uses maven, and so is out of date.