bzip2 is a freely available, patent free, data compressor.
 .
 bzip2 compresses files using the Burrows-Wheeler block-sorting text
 compression algorithm, and Huffman coding. Compression is generally
 considerably better than that achieved by more conventional
 LZ77/LZ78-based compressors, and approaches the performance of the PPM
 family of statistical compressors.
 .
 The archive file format of bzip2 (.bz2) is incompatible with that of its
 predecessor, bzip (.bz).