Only thing I can vouch for is syncthing, which is a little more setup
but worth it. You don't get a webGUI to actually view and download files
though, only to manage clients.
So it kind of depends on your use case - what is device A and what is
device B that people want to sync between? Is it a laptop and phone? Do
you need online login?
Another one I have tried is Seafile, but it needs a DB (but it does do
SQLite...). It had fewer features back when I used it, but it was
focused heavily on file sharing which was nice. I like it more than
nextcloud for performance.