If you're looking for an open-source self-hosted alternative to Dropbox, I've found Seafile to be flawless. Seadrive is also nice if you want to access your data as if it were a network drive. * Not affiliated with seafile, just really like their software. https://www.seafile.com/
I switched after Dropbox started imposing a device limit. There was a but of a learning curve to get it all set up and the quality of the client software can be hit-or-miss. That said, the core functionality (syncing files between devices) has been rock solid.