From your list I can recognize only ST, borgbackup and rsync/rclone, the others are described too vaguely. Borgbackup is not for Android (there is an attempt), rsync is with limitations. All can be installed on Synology NAS. Borgbackup and rsync use SSH, ST is better in this regard. Also, Borgbackup and rsync are command-line tools, there’s no GUI (at least not for Synology). Etc.
@all But the most important point for me is that I have various kinds of folders (not only photos), and I do not want to use different tool for every type of folder. For instance, I was hesitating whether only to mirror a particular folder to NAS from my notebook, or whether to share this folder with other notebooks and use bi-directional synchronization. If I change my mind, why would I have to use another tool?
ST is advertised as “a continuous file synchronization program. It synchronizes files between two or more computers in real time, safely protected from prying eyes.”. I do not understand how one-way synchronization contradicts this motto. Wikipedia says (File synchronization - Wikipedia):
File synchronization (or syncing ) in computing is the process of ensuring that computer files in two or more locations are updated via certain rules.
In one-way file synchronization , also called mirroring, updated files are copied from a source location to one or more target locations, but no files are copied back to the source location. In two-way file synchronization , updated files are copied in both directions, usually with the purpose of keeping the two locations identical to each other. In this article, the term synchronization refers exclusively to two-way file synchronization.
So attempts to persuade us that one-way sync is not a sync are based on bad foundations.