[justusthane]

It's not cloud storage, but I can't recommend SyncThing enough. Syncs selected local folders between any/all of your devices whenever they're able to contact each other.

I use it specifically to keep my files out of the cloud, but in the past I've also installed it on a DigitalOcean instance and had it function sort of like cloud storage that way.

My favorite thing about it is that you're selecting existing local folders to sync rather than moving files to a special "sync" directory, meaning it's very flexible in what you can do with it (syncing dot files between machines, as one example).

The only problem is there's no good iOS client yet, but macOS, Windows, Linux, Android are all supported.