Based on components of the Microsoft Sync Framework ... supports complex scenarios like combining files from two folders in one case, and mimicing renames and deletes in another case... can be installed by non-admins *if* the Sync Framework is preinstalled
As a thank you to the community ... offering free accounts ... the (normally) $10 monthly account (250 GB) absolutely free "for life" if created before May 15th...
Connect to WebDAV, FTP, Amazon S3, FTPS, or SFTP servers through a virtual drive which is a full file-system drive which works in DOS, PowerShell, etc.