CloudMounter started on the Mac and built its reputation there: mount Google Drive, Dropbox, OneDrive, S3 and FTP/SFTP as a drive so they behave like local storage. It has a Windows version too, and it is a polished take on the mounting idea. FTPie comes at the same problem from the file-manager side, and is built for Windows first.
The core distinction is the same as with any mounter: CloudMounter makes remote storage look local; FTPie gives you a workspace to manage it. The secondary distinctions are platform focus and pricing - CloudMounter leans subscription, FTPie is a one-time purchase.