Owncloud client https://owncloud.com/
We use it to connect to our own server for storing receipts, plane tickets, company documentation etc. It's great to keep things synced between devices.
A similar thing is #syncthing, which is cross platform although I don't have a use case for it at the moment, sadly. https://syncthing.net
@Yglorba
Good question. I guess people thought naively that .sfv files were enough, but of course that's not true.
Some .nfo files contain md5s for things, but that would be easily changeable.
It would have to be a cryptographic checksum, using something like GPG/PGP with a distributed fingerprint to be any good.
I've seen one or two over the years, but not as many as you'd expect for people that should be worried about security and image.