A Microsoft file hosting and synchronization service.
Thanks for the info about pCloud JanTerjeAugestad ... having paid for a monthly subscription to Google Drive and uploaded all my files, I found that it was using a huge amount of hard drive space for cache files (noticed in my system data under 'About this Mac/Storage'). I stupidly tried deleting the cache files to free up the hard drive space they were taking up, but they then had to resync, meaning that they were all redownloaded to my hard drive! So I thought I'd check out pCloud. I moved all my files from GD to pCloud and once I'd uninstalled GD and deleted all files from GD, my system data went down from >400 GB to currently 55 GB. Obviously pCloud handles cache files in a very different way to GD!
Once my files were uploaded (took a weekend to upload all 400 GB), pCloud has since been working smoothly and I've had no hassles at all with syncing. My files are safely stored on my hard drive and backed up to pCloud - exactly how OneDrive used to work before MS broke it.