bzip2 is another open source lossless data compression algorithm that was originally released in the mid 90s and then once again in 2000 as a more stable version.
The compression's author is Julian Seward.
It is simply a data compressor, unlike RAR and ZIP, which are archivers as well.
The big knock is speed, for which it is very slow, however actually compression is very good. Those looking for faster compressor, should use zlib.