Looking for Dropbox alternatives a few weeks ago, I found a consultant talking about Amazon as a competitor. Lo and behold, there’s an Amazon Workdocs buried at AWS.

It’s $5/mo per head, 1TB of storage, Mac and PC clients. It is rough around the edges (nomobile ecosystem, for example) but it seems to be more than adequate for syncing and some sharing.

[0] https://aws.amazon.com/workdocs/

Why wouldn't Google Drive or Microsoft OneDrive be comparable? They also have online multiplayer document editing experience built in.