I've heard of Nexcloud. What's the difference between it and Syncthing?
syncthing is like dropbox. Nextcloud is remote storage you can access, with tons of plugins to do additional things with it too, like video chat for example.
Nextcloud is more like Dropbox imho. It has a web interface, but there are also sync clients and you need a webserver to host your stuff.
Nextcloud is not like Dropbox out of the box (no pun intended). While Syncthing is pretty much what Dropbox's core service used to be.