Gzip
gzip is short for GNU ZIP, a GNU free software replacement for the Unix compress program.
Gzip is based on the deflate algorithm, which is a combination of LZ77 and Huffman coding. 'Deflate' was developed in response to patents that covered LZW and other compression algorithms and limited the usability of 'compress' and other popular archivers.
Gzip should not be confused with ZIP, with which it is not compatible. Gzip doesn't archive files, it only compresses them, which is why it is often seen in conjunction with a separate archiving tool (most popularly tar).
In order to make it easier to develop software that uses compression, the zlib library was created. It supports the gzip file format and 'deflate' compression. The library is widely used, because of its small size, efficiency and versatility. Both gzip and zlib were written by Jean-Loup Gailly and Mark Adler. Since the late-1990s there has been some movement from gzip to bzip2 which produces considerably smaller files under many circumstances but is also considerably slower.
The zlib compressed data format, the 'deflate' algorithm and the Gzip file format were standardised respectively as RFC 1950, RFC 1951 and RFC 1952.
The usual file extension for gzipped files is .gz. Unix software is often distributed as files ending with .tar.gz or .tgz, called tarballs. They are files first packaged with tar and then compressed with gzip. They can be decompressed with gzip -d file.tar.gz or unpacked with tar xzf file.tar.gz. Nowadays more and more software is also distributed as .tar.bz2 archives because of the advantages of bzip2 compression.
AdvanceCOMP implements a deflate implementation which allows to recompress .gz files to make them even smaller than gzip is capable of.