The Z Shell is covered by the following copyright notice.
The Z Shell is copyright (c) 1992-2007 Paul Falstad, Richard Coleman, Zoltán Hidvégi, Andrew Main, Peter Stephenson, Sven Wischnowsky, and others. All rights reserved. Individual authors, whether or not specifically named, retain copyright in all changes; in what follows, they are referred to as `the Zsh Development Group'. This is for convenience only and this body has no legal status. The Z shell is distributed under the following licence; any provisions made in individual files take precedence.
Permission is hereby granted, without written agreement and without licence or royalty fees, to use, copy, modify, and distribute this software and to distribute modified versions of this software for any purpose, provided that the above copyright notice and the following two paragraphs appear in all copies of this software.
In no event shall the Zsh Development Group be liable to any party for direct, indirect, special, incidental, or consequential damages arising out of the use of this software and its documentation, even if the Zsh Development Group have been advised of the possibility of such damage.
The Zsh Development Group specifically disclaim any warranties, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. The software provided hereunder is on an "as is" basis, and the Zsh Development Group have no obligation to provide maintenance, support, updates, enhancements, or modifications.