Syncthing is a great tool. It's like Dropbox, but good. [1]
One thing missing in the usual setup however is an off-site node to ensure survivability of backups.
I've been contemplating building a service that offers just that, using a major cloud provider and charging users proportional to resource usage.
Would there be interest in such an offering?
[1] https://tonsky.me/blog/syncthing/