Sync Hive and Dropbox to attach files to actions, projects, action templates, share them in messages, and anywhere else file attachment is supported. All file stores do not store the actual files in Hive, but rather a sign post of them. Users can have as many file stores integrated as they would like, but they can only link 1 account per service; in other words, you can have 1 Dropbox account and 1 Google Drive etc. but I can not have 2 Dropbox accounts hooked up.
Other users can only see your files if you attach/share them with the user in Hive and they have permission to see it in the respective cloud storage service.