Ask HN: MIT/BSD/Apache cloud file sync?

What are some permissively licensed file syncing solutions?

Ideally I'm looking for something that allows me to setup one (or more) directories on a computer and recursively sync to other computers, and into some form of cloud storage for backup.

I'm aware of OwnCloud, NextCloud, Resilio Sync etc. However, I'm specifically interested in permissively licensed software.

Syncthing looks really nice, and I can handle an MPL license, but it presently lacks cloud sync and specifically recommends using additional software for backup.

I recognise I'm asking a lot, and am prepared to try out (and contribute to) incomplete projects if anyone knows of WIP projects on GitHub etc.