This is Debian GNU/Linux's prepackaged version of xzip.

This package was put together by me, Daniel Schepler
<schepler@debian.org> from the original sources in
ftp.gmd.de:/if-archive/infocom/interpreters/zip/xzip182.tar.Z
based on Mark Baker's original packaging.

The program is copyright 1996 Andrew Plotkin.
It is based on Zip 2.0.7, copyright 1996 Mark Howell.
This debian package is copyright 1997 Mark Baker,
copyright 2001 Daniel Schepler.

The copyright notice on it, taken from the manual page, is:

You are expressly forbidden to use this program on an Infocom game data file 
if, in so doing, you violate the copyright notice supplied with the original 
Infocom game.

Parts of this program (the files xinit.c, xio.c, xkey.c, xmess.c, xstat.c,
xtext.c) are copyrighted by Andrew Plotkin. These files may be distributed,
modified, and used freely, with the exception noted above.

I do not know the exact copyright status of the rest, except that it was
written by Mark Howell and thus is probably copyrighted by him. He released
it for free, so to the best of my knowledge, it can also be distributed,
modified, and used freely, with the exception noted above.