You can also try ownCloud [0] which can be installed on a LAMP server and has possibility to access from all platforms with both syncing and mounting. You can also hook in existing storage as backend.
I use both owncloud & syncthing, but they serve different needs. I use OwnCloud to share stuff with friends an family, but I use syncthing for syncing stuff across my "fleet". The main advantage of syncthing is that it runs standalone even on servers where I have no privileges.
[0] https://owncloud.org/