A Microsoft file hosting and synchronization service.
Same problem here. After having one of our family accounts have no OneDrive access for other 24 hours (Without warning before, or during the outage and only finding out after looking it up online). We now find we can't share files between it each other. Even worse shared folders are now being duplicated on multiple machines, named as that machines.
Wasn't the whole point of OneDrive to avoid this, keeping everything in sync!