JRuby is released under a tri CPL/GPL/LGPL license. You can use it,
redistribute it and/or modify it under the terms of the:

 CPL - see COPYING.CPL file
 GPL - see COPYING.GPL file 
 LGPL - see COPYING.LGPL file

Some additional libraries distributed with JRuby are not covered by
JRuby's licence. See the licence files for the respective libraries in
the 'lib' directory for more information and also LICENSE.RUBY for most
files found in src/lib/ruby/1.8.