sync-mht (hackage): A command line tool that can be used to incrementally synchronize a directory hierarchy with a second one. It is using a Merkle-Hash-Tree to compare the folders, such that the synchronization time and communication (round) complexity grows only logarithmically with the size of the directories (assuming the actual difference of the directories is small).  The communication happens through standard streams between parent and child processes, which can easily be routed through remote command execution tools.
Keywords: library|mit|program|utility|communication|directory-hierarchy|synchronization