A Microsoft file hosting and synchronization service.
I feel everyone's pain here. I struggled for about a week, and then ultimately made the decision a few days ago to migrate elsewhere. It was the right decision.
Microsoft has gone radio silent because this was an intentional change as part of a broader business plan. They're not going to revert back to the way it was. They're just Justin Trudeau'ing the thread hoping it'll go away. The ball is in the users' court, whether you like it or not.