sftp (ssh) works out of the box with the GUI shell (nautilus?) on most GNU/Linux distros. It just looks like a network drive.

webdav is the same but ALL popular OSes support it, I really don't understand why more people don't use that as it doesn't get any simpler. You don't even need a browser.

EDIT: the reply here is dead (?) I don't agree with it (really at all, IMO google drive has one of the worst most confusing UIs ever, that seems to be an intensely objective thing) but some others might and I don't find it offensive:

>I couldn't use webdav without going to find out how to use webdav.

>I can figure out google drive in a minute. So can she. So can her paying customers.