A Microsoft file hosting and synchronization service.
I'm not gonna go for an alternative without further research. I already own a piece of software which allows me to sync between different machines on my network at home/office. Since it's only me that needs syncing and it involves two machines the number of permutations is not that big (either with more people or more machines it gets complicated really fast).
I also own a piece of software which helps me mounting onedrive as a networkdisk. So my heavily encrypted backups are on onedrive. Which works because you can select (still; but maybe that is also going to disappear :-( ) which directories not to sync. That is the biggest difference between onedrive and icloud and why icloud is useless. I pay for the diskspace so why not use it?