Rzip
rzip is an archiving format (implemented for Unix-style operating systems) that achieves better compression than other formats by taking advantage of long-distance redundancies in the full data set being compressed. Due to its need to analyze the data set as a whole before compressing any of it, it is unable to work with a "piped" data stream (as opposed to a set of disk files), and requires a large amount of memory and a slow, multi-pass algorithm.
There does not appear to be any written-up detailed documentation of the file format in any public place, but the program is open-source, allowing enterprising geeks to figure out the format by studying the code.
lrzip is an improved archiving format adapted from rzip, but not compatible with it.
