GNU Zip (or ''gzip'' for short) is a stream compression program (like the UNIX [compress] program), and not an archiver (like the DOS [pkzip] program) that uses an ''unpatented'' (and unpatentable) algorithm for its compression.  The program [bzip] can compress even more, but takes more memory to do so.  The [zlib] library uses the same algorithms, and can be used to process or produce gzipped files (IIRC, though there might be a header too.)