File archive compressed using gzip (GNU zip) compression; used by Unix-based systems and replaces the older "compress" algorithm; offers better compression and does not use patented algorithms.
Most GZIP files use the .GZ file extension.
Program(s) that open gzi files
Mac: Smith Micro StuffIt Deluxe for Mac; MacGzip Windows: Smith Micro StuffIt Deluxe for Windows; ConeXware PowerArchiver; Corel WinZip; 7Zip; Win-GZ
Unix: gzip
Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/gzi