Xgdvi is a free software and distributed freely. It is a part of software in the TEX -Guy package and its Web site is as follows:
http://TypeHack.aial.hiroshima-u.ac.jp/TeX-Guy/
The primary FTP site is as follows:
ftp://TypeHack.aial.hiroshima-u.ac.jp/
The TEX -Guy package requires VFlib 3.6. It can be obtained at the following URL:
http://TypeHack.aial.hiroshima-u.ac.jp/VFlib/
ftp://TypeHack.aial.hiroshima-u.ac.jp/pub/