...If you are looking for that, BorgBackup and restic are good options as of 2024.
Warning! Old 1.x versions of bKappa are insecure. Do not use them. Because backup metadata is serialized with the "pickle" Python module (https://docs.python.org/2.7/library/pickle.html), a malicious backup can take over your machine.
Cyclone is an easy to use, one- or two-way synchronization tool. It use a clean command-line interface. It aims to be compact (less than 10 Ko) and cross-platform (as it is coded in standard python).