Consistent Archive Tree
Despite it's considerable age, Tape ARchive format (tar) is still in widespread use. This is unfortunate because has as several features that are footguns in a modern context.
Firstly, because it contains timestamps (ctime, mtime) then archiving the same files twice will give a tar file that has a few bytes different, and thus will have a different hash. creating a archive deterministically was not a priority when tar was designed.