A Microsoft file hosting and synchronization service.
Same thing has happened to me last night. Saved everything locally before transferring stuff to the new personal vault. Personal vault broke halfway through files being uploaded. Tried to delete files from personal vault to start it again and my local backups and Onedrive originals got wiped.
I'd also already cleared the onedrive recycle bin as i thought the local files were safe.
Bye bye 7 years of photos/documents