Pure network drives just aren’t as awesome as working locally, and synchronising changes globally. Realising this is why the Dropbox founders are now rich. Well done them. Dependence on single remote servers for every trifling step is stupid. Git has shown us that for code - and for that matter, distributed databases have shown us that for the rest of the data. (Hello google.) 
|||For that matter, git also has a file-syncing extension called git-lfs.|
Peer to peer is more robust. (Taking it still further, how about everything be sneakernets?)
Anyway, file synchronising is handy, and tricky to do.
File storage/sync/sharing is tricky. I have been using Dropbox, but their technical and legal shortcomings are laughably bad. More secure alternatives:
an in-principle secure alternative is keybase, although it’s not quite syncing, it’s a kind of syncing-rebooted thing.
SpiderOak is the most popular encrypted service, although still based in the USA, which, like Russia and China, is more of a secret service browsing library than a secure document store where you would keep actual private stuff.
“sparkleshare creates a special folder on your computer. You can add remotely hosted folders (or “projects”) to this folder. These projects will be automatically kept in sync with both the host and all of your peers when someone adds, removes or edits a file.”
syncthing has an elegant design, although still a little too intrusively technical.
- Private. None of your data is ever stored anywhere else than on your computers. There is no central server that might be compromised, legally or illegally.
- Encrypted. All communication is secured using TLS. The encryption used includes perfect forward secrecy to prevent any eavesdropper from ever gaining access to your data.
- Authenticated. Every node is identified by a strong cryptographic certificate. Only nodes you have explicitly allowed can connect to your cluster.
Academic cred: “Ori is a distributed file system built for offline operation and empowers the user with control over synchronization operations and conflict resolution. We provide history through light weight snapshots and allow users to verify the history has not been tampered with. Through the use of replication instances can be resilient and recover damaged data from other nodes.”
Tresorit is a Swiss Spideroak competitor, which capitalises on stronger Swiss privacy laws, (YMMV) as well as trendy encryption technology. Closed-source though, so there is still a degree of blind faith.
git-annex I have not yet tried, but it supports explicit and customisable folder-tree synchronisation, merging, and sneakernets and as such I am excited by it.
mega is a surprsingly good semi-open source, host-blind encryption business from New Zealand. The UI is occasionally freaky but it’s reasonable especially for its bargain-basement price.
Listing encrypted backups only, because I ma not crazy.
Also, I’m only listing open-source options or ones not in a jurisdiction with poor privacy laws, such as China, Russia or the USA.
Windows, OSX, Linux, duplicati:
Duplicati works with standard protocols like FTP, SSH, WebDAV as well as popular services like Microsoft OneDrive, Amazon Cloud Drive ” S3, Google Drive, box.com, Mega, hubiC and many others.
Features Backup files and folders with strong AES-256 encryption. Save space with incremental backups and data deduplication. Run backups on any machine through the web-based interface or via command line interface. Duplicati has a built-in scheduler and auto-updater.
OSX, linux, more bare-bones, duplicity:
Duplicity backs directories by producing encrypted tar-format volumes and uploading them to a remote or local file server. Because duplicity uses librsync, the incremental archives are space efficient and only record the parts of files that have changed since the last backup. Because duplicity uses GnuPG to encrypt and/or sign these archives, they will be safe from spying and/or modification by the server.
Linux, OSX, tarsnap. comes with a server for $0.25/gb/month:
Tarsnap is a secure, efficient online backup service:
Encryption: your data can only be accessed with your personal keys. We can’t access your data even if we wanted to! Source code: the client code is available. You don’t need to trust us; you can check the encryption yourself! Deduplication: only the unique data between your current files and encrypted archives is uploaded. This reduces the bandwidth and storage required, saving you money! Tarsnap runs on UNIX-like operating systems (BSD, Linux, MacOS X, Cygwin, etc)